HPLC-MS/MS measurement of lidocaine in rat skin and plasma. Application to study the release from medicated plaster.

A simple, sensitive HPLC-MS/MS method was developed and validated for the determination of lidocaine in skin and plasma of rats. The methods were established and validated assessing lower limit of quantitation (LLOQ), linearity, intra and inter-day precision and accuracy, selectivity, recovery and matrix effect. Chromatography was done on a Gemini column embedded with C18 stationary phase (50 mm × 2.0 mm, 5 µm particle size), using a gradient with mobile phases consisting of 0.1% HCOOH in bidistilled water and 0.1% HCOOH in acetonitrile. The mass spectrometer worked with electrospray ionization in positive ion mode and selected reaction monitoring, using target ions m/z 235.10 for lidocaine and m/z 245.10 for lidocaine-d10, used as internal standard. RESULTS: The linearity of the method was in the ranges of lidocaine concentrations 10.0-200.0 ng/mL for skin homogenate (accuracy 94.1-105.5%; R2 ≥ 0.998) and 0.025-2 ng/mL for plasma (accuracy 96.2-104.8%; R2 ≥ 0.996). The intra- and inter-day precision and accuracy determined on three quality control samples (20, 75 and 170 ng/mL for skin and 0.075, 0.4 and 1.5 ng/mL for plasma) were ≤4.2% and 103.8-108.2% for skin and ≤12.4% and 95.5-101.4% for plasma. The LLOQ was 10 ng/mL in skin homogenate and 0.025 ng/mL in plasma. The applicability of the method was demonstrated by measuring lidocaine in skin and plasma after exposure to medicated patches containing 5% lidocaine.

Activation of the SDF1/CXCR4 pathway retards muscle atrophy during cancer cachexia.

Cancer cachexia is a life-threatening syndrome that affects most patients with advanced cancers and causes severe body weight loss, with rapid depletion of skeletal muscle. No treatment is available. We analyzed microarray data sets to identify a subset of genes whose expression is specifically altered in cachectic muscles of Yoshida hepatoma-bearing rodents but not in those with diabetes, disuse, uremia or fasting. Ingenuity Pathways Analysis indicated that three genes belonging to the C-X-C motif chemokine receptor 4 (CXCR4) pathway were downregulated only in muscles atrophying because of cancer: stromal cell-derived factor 1 (SDF1), adenylate cyclase 7 (ADCY7), and p21 protein-activated kinase 1 (PAK1). Notably, we found that, in the Rectus Abdominis muscle of cancer patients, the expression of SDF1 and CXCR4 was inversely correlated with that of two ubiquitin ligases induced in muscle wasting, atrogin-1 and MuRF1, suggesting a possible clinical relevance of this pathway. The expression of all main SDF1 isoforms (α, ß, γ) also declined in Tibialis Anterior muscle from cachectic mice bearing murine colon adenocarcinoma or human renal cancer and drugs with anticachexia properties restored their expression. Overexpressing genes of this pathway (that is, SDF1 or CXCR4) in cachectic muscles increased the fiber area by 20%, protecting them from wasting. Similarly, atrophying myotubes treated with either SDF1α or SDF1ß had greater total protein content, resulting from reduced degradation of overall long-lived proteins. However, inhibiting CXCR4 signaling with the antagonist AMD3100 did not affect protein homeostasis in atrophying myotubes, whereas normal myotubes treated with AMD3100 showed time- and dose-dependent reductions in diameter, until a plateau, and lower total protein content. This further confirms the involvement of a saturable pathway (that is, CXCR4). Overall, these findings support the idea that activating the CXCR4 pathway in muscle suppresses the deleterious wasting associated with cancer.

Oleamide-mediated sleep induction does not depend on perturbation of membrane homeoviscosity.

To verify whether the sleep-inducing properties of oleamide were related to its ability to perturb membrane homeoviscosity, affecting 5-HT(2A) receptors, we compared the effects of oleamide and oleic acid, the latter lacking both the sleep-inducing effect and the action on 5-HT(2A) receptors. In binding studies the two compounds did not directly interact with rat brain cortex 5-HT(2A) receptors, nor did they increase the affinity of a 5-HT(2A) agonist, either in vitro or ex vivo. They had similar fluidizing effects, in vitro at high concentrations (>/=10 microM), and ex vivo after a dose of 100 mg/kg, and they reduced locomotor activity with similar potency. There thus appears to be no causal relationship between the fluidizing effects of oleamide and its sleep-inducing properties.

Cocaine-seeking behavior in response to drug-associated stimuli in rats: involvement of D3 and D2 dopamine receptors.

Previous studies employed a second-order schedule paradigm maintained by cocaine reinforcement to show that BP897, a dopamine D(3) partial agonist, selectively modulated drug-seeking behavior. We investigated its effect on drug-seeking behavior induced by presentation of stimuli associated with and predictive of cocaine availability after a period of extinction and in the absence of any further cocaine. Male rats were trained to associate discriminative stimuli (S(D)) with the availability of intravenous (i.v.) 0.25 mg/0.1 ml/infusion cocaine (S(D+)) or no-reward (S(D-)) saline solution. Each infusion of cocaine or saline was followed by a response-cue signaling 20-s time-out (TO). After meeting the self-administration training criterion rats were placed on extinction conditions during which i.v. solutions and S(D)s were withheld. Every other 3 days on which rats met the extinction criterion, reinstatement tests were conducted, presenting the S(D+) or S(D-) noncontingently together with a contingent presentation of cocaine- or saline-cues signaling 20-s TO. Regardless of the order of presentation or the nature of the stimuli (auditory or visual), cocaine-associated but not saline-associated stimuli reinstated responding on the previously active lever. Presentation of cocaine-associated stimuli induced lasting drug-seeking behavior for at least eight test sessions. BP897 (1.0 mg/kg i.p.) significantly attenuated this behavior. Since it has been reported that BP897 can interact with a panel of different receptors with high affinity, we evaluated the effects of 7-OH-DPAT, an agonist to D(3) receptors, raclopride, a preferential antagonist to D(2) receptors, and WAY 100,635, an antagonist at 5-HT(1A) receptors, on drug-seeking behavior. 7-OH-DPAT (0.1-3.0 mg/kg i.p.) had biphasic effects on reinstatement induced by the cocaine-associated cues, low dosages reducing and high dosages increasing the impact of cocaine-associated stimuli on rats' behavior. Raclopride (0.1, 0.3 mg/kg s.c.) completely prevented drug-seeking behavior induced by the reintroduction of cocaine-associated stimuli. WAY 100,635 (0.1-1.0 mg/kg s.c.) had no effect on this behavior. These results, while confirming that the partial agonist at the D(3) receptors, BP897, might be a useful medication, also suggest a role of D(2) receptors in cue-induced cocaine-seeking behavior.

Evidence that dopamine mechanisms in the nucleus accumbens are selectively involved in the effect of desipramine in the forced swimming test.

Bilateral injections of 5 or 1 (but not 0.5) micrograms sulpiride into the nucleus accumbens reduced the effect of a 7-day treatment with 10 mg/kg/day desipramine in the forced swimming test. Bilateral injections of 5 or 1 micrograms sulpiride in the caudate-putamen did not modify the anti-immobility effect of desipramine. The data support the hypothesis that dopamine mechanisms in the limbic regions of the brain of the rat are involved in the effect of repeated treatment with desipramine in the forced swimming test.

The role of serotonin and dopamine in brain in the antidepressant-like effect of clonidine in the forced swimming test.

The effect of clonidine (0.1 mg/kg, i.p.), as a three-injection course, on behaviour in the forced swimming test was studied in rats injected intracerebroventricularly (i.c.v.) with 150 micrograms 5,7-dihydroxy-tryptamine (5,7-DHT) to destroy serotonin (5-HT) neurones or treated with 100 mg/kg (i.p.) (+/-)-sulpiride or 0.5 micrograms/0.5 microliter (-)-sulpiride in the nucleus accumbens. Clonidine significantly increased struggling and reduced floating and the effects were antagonized by both treatments with sulpiride but not by 5,7-DHT which markedly depleted 5-HT in brain. The results suggest that the mesolimbic dopaminergic system but not 5-HT neurones, plays a permissive role in the antidepressant-like effect of clonidine in the forced swimming test.

8-Hydroxy-2-(di-n-propylamino) tetralin, a selective serotonin1A receptor agonist, blocks haloperidol-induced catalepsy by an action on raphe nuclei medianus and dorsalis.

The selective serotonin1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) was studied for its ability to reverse haloperidol-induced catalepsy in rats. Given subcutaneously 8-OH-DPAT (0.06-0.5 mg/kg), dose-dependently antagonized the catalepsy induced by 1 mg/kg of haloperidol. Intraventricular injection of the serotonin (5-HT) neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), which caused marked depletion of 5-HT in brain, did not change haloperidol-induced catalepsy per se, but completely antagonized the anticataleptic effect of subcutaneously administered 8-OH-DPAT. When injected directly into the median or dorsal raphe nucleus, 8-OH-DPAT, in doses ranging from 0.2 to 5 micrograms/0.5 microliter, reduced the catalepsy induced by haloperidol. The results suggest that the activation of 5-HT1A receptors, probably those located presynaptically on 5-HT-containing cell bodies, reduces the catalepsy induced by haloperidol.

Roles of 5-HT(1A) receptors in the dorsal raphe and dorsal hippocampus in anxiety assessed by the behavioral effects of 8-OH-DPAT and S 15535 in a modified Geller-Seifter conflict model.

8-OH-DPAT [8-hydroxy-2-(di-N-propylamino)tetralin], a 5-HT(1A) receptor agonist, and S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine, a partial agonist at 5-HT(1A) receptors, were administered into the dorsal raphe nucleus and dorsal hippocampus and their behavioral effects were assessed in a modified Geller-Seifter conflict model. Injected into the dorsal raphe nucleus 8-OH-DPAT, 1 microg but not 0.04 or 0.2 microg 0.5 microl(-1), and S 15535, 2.5 microg but not 0.1 or 0.5 microg 0.5 microl(-1), significantly increased punished responding with no effect on rates of unpunished or time-out responding. WAY 100635, a selective 5-HT(1A) receptor antagonist, injected subcutaneously at 0. 3 mg kg(-1) 30 min before 1 microg 8-OH-DPAT or 2.5 microg S 15535 in the dorsal raphe, completely antagonized their effects on punished responding. At doses ranging from 1 to 10 microg microl(-1) injected into the CA1 region of the dorsal hippocampus neither 8-OH-DPAT nor S 15535 modified punished responding or the rates of time-out. At the highest doses, 8-OH-DPAT significantly reduced unpunished responding whereas S 15535 had the opposite effect. The results suggest that stimulation of 5-HT(1A) receptors in the dorsal raphe nucleus has anxiolytic-like effects whereas stimulation of postsynaptic receptors in the dorsal hippocampus has no anxiolytic or anxiogenic effects, at least judging from changes in rates of punished responding. These results are compatible with the hypothesis that 5-HT(1A) receptor agonists and partial agonists attenuate anxiety by reducing serotonergic transmission in brain areas innervated by the dorsal raphe nucleus.

Pyrroloquinoxaline derivatives as high-affinity and selective 5-HT(3) receptor agonists: synthesis, further structure-activity relationships, and biological studies.

The synthesis, pharmacological evaluation, and structure-activity relationships (SARs) of a series of novel pyrroloquinoxalines and heteroaromatic-related derivatives are described. The new pyrroloquinoxaline-related ligands were tested in rat cortex, a tissue expressing high density of 5-HT(3) receptors, and on NG108-15 cells and exhibited IC(50) values in the low nanomolar or subnanomolar range, as measured by the inhibition of [(3)H]zacopride binding. The SAR studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1, L2, and L3 in the 5-HT(3) receptor cleft, while the 7-OH pyrroloquinoxaline analogue was designed to investigate hydrogen bonding with a putative receptor site H1 possibly interacting with the serotonin hydroxy group. The most active pyrroloquinoxaline derivatives showed subnanomolar affinity for the 5-HT(3) receptor. In functional studies ([(14)C]guanidinium accumulation test in NG108-15 hybrid cells, in vitro) most of the tested compounds showed clear-cut 5-HT(3) agonist properties, while some others were found to be partial agonists. Several heteroaromatic systems, bearing N-substituted piperazine moieties, have been explored with respect to 5-HT(3) affinity, and novel structural leads for the development of potent and selective central 5-HT(3) receptor agonists have been identified. Preliminary pharmacokinetic studies indicate that these compounds easily cross the blood-brain barrier (BBB) after systemic administration with a brain/plasma ratio between 2 and 20, unless they bear a highly hydrophilic group on the piperazine ring. None of the tested compounds showed in vivo anxiolytic-like activity, but potential analgesic-like properties have been possibly disclosed for this new class of 5-HT(3) receptor agonists.

Evidence that 5-hydroxytryptamine in the forebrain is involved in naloxone-precipitated jumping in morphine-dependent rats.

A withdrawal syndrome was precipitated by naloxone in morphine-dependent rats injected with 5,7-dihydroxytryptamine (5,7-DHT) in the ventromedial tegmentum (VMT) at the level of the nucleus interpeduncularis. 5,7-DHT, which markedly depleted 5-hydroxytryptamine (5-HT) in the forebrain but not in the brainstem, significantly reduced jumping in abstinent rats with no significant effect on other withdrawal signs. The effect of morphine 10 mg kg-1 on responses on the hot plate was unchanged in 5,7-DHT-treated rats. The findings suggest that 5-HT in the forebrain is selectively involved in the jumping of morphine-abstinent rats.

Brain-to-blood partition and in vivo inhibition of 5-hydroxytryptamine reuptake and quipazine-mediated behaviour of nefazodone and its main active metabolites in rodents.

The brain/plasma partition of nefazodone, hydroxynefazodone (OHNFZ) and m-chlorophenyl-piperazine (mCPP) and their antagonism of p-chloroamphetamine (PCA)-induced 5-hydroxytryptamine (5-HT) depletion and quipazine-induced head twitches were compared in rodents. Nefazodone (30 mg kg(-1), i.p.) rapidly entered the brain but concentrations were exceeded by mCPP, the metabolic ratio being 47 and 10 in the mouse and rat respectively. OHNFZ was detectable in plasma but never in brain. Brain concentrations of OHNFZ in the mouse (30 mg kg(-1), i.p.) were less than 10% of those in plasma, confirming a poor blood-brain barrier penetration. Concentrations of its metabolite mCPP were similar to those after 5 mg kg(-1)(i.p.) mCPP. In the mouse, nefazodone (30 mg kg(-1)) antagonized the 5-HT depleting effect of PCA 2 h after dosing, when it had disappeared from brain but when mCPP concentrations were similar to those after 5 mg kg(-1) (i.p.) mCPP. However, mCPP antagonized PCA less than nefazodone. In the rat, nefazodone pretreatment (30 mg kg(-1), 15 min) prevented (97% of inhibition) quipazine-induced head twitches. The effect was weaker (65% of inhibition) but significant when only mCPP was detected in brain. Analysis of brain concentrations of the two compounds after their ED50 against quipazine indicated that both contributed to the effect, although nefazodone was more active than mCPP in terms of concentrations required to obtain a comparable reduction of twitches. These findings show that mCPP concentrates in the brain following injection of nefazodone and may play a role in preventing quipazine-induced behaviour and PCA-induced 5-HT depletion. In contrast OHNFZ poorly enters the brain and its in vivo activity is mostly due to its biotransformation to mCPP.

Effect of chronic treatment with 8-OH-DPAT in the forced swimming test requires the integrity of presynaptic serotonergic mechanisms.

The effect of chronic treatment with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on rats' behaviour in the forced swimming test was studied in animals injected intracerebroventricularly with 150 micrograms 5,7-dihydroxytryptamine (5,7-DHT) or given three oral doses of parachlorophenylalanine (PCPA). A single dose of 0.25 mg/kg 8-OH-DPAT significantly reduced rats' immobility in 5,7-DHT-sham-operated animals 24 h after a 14-day schedule of 0.25 mg/kg 8-OH-DPAT or saline subcutaneously twice daily. The effects of acute 8-OH-DPAT in both chronically 8-OH-DPAT- and saline-treated animals were prevented by 5,7-DHT which caused a marked depletion of brain serotonin (5-HT). Since animals treated with both 8-OH-DPAT and 5,7-DHT were more active in an open field than those receiving the substances separately, the forced swimming behaviour was analyzed in more detail in subsequent experiments. PCPA treatment completely prevented the increase in struggling caused by acute and chronic 8-OH-DPAT, administered as in the previous experiment, but did not modify the reduction of floating caused by 8-OH-DPAT. PCPA and 8-OH-DPAT, alone or in combination, did not modify rats' activity in an open field. Finally, 0.5 and 1.0 micrograms 8-OH-DPAT in the nucleus raphe dorsalis significantly increased struggling and reduced floating to the same extent in animals which had received 0.25 mg/kg 8-OH-DPAT or saline subcutaneously twice daily for 14 days. It thus appears that the antidepressant-like effects of chronic treatment with 8-OH-DPAT in the forced swimming test require the integrity of presynaptic serotonergic mechanisms.

Effects of central dopamine depletion on the d-amphetamine discriminative stimulus in rats.

The discriminative stimulus properties of d-amphetamine, cocaine, and apomorphine were assessed in rats trained in a two-lever, food-reinforced drug discrimination paradigm to discriminate 1.0 mg/kg d-amphetamine from saline. After determination of these dose-response relationships, the rats were divided into two groups. One group (6-OHDA) was given injections of desmethylimipramine (DMI, 30 mg/kg, IP) and 6-hydroxydopamine (6-OHDA, 100 micrograms/10 microliters each ventricle), while the other group (sham) was given the same dose of DMI and 6-OHDA vehicle (intraventricularly). Beginning approximately 45 days after intraventricular injections, dose-response relationships were redetermined for all three drugs. Larger doses of d-amphetamine were required to elicit the same response in the 6-OHDA group (i.e. the dose-response relationship was shifted to the right), while no change was observed in the sham group. Any changes in the dose-response relationships for cocaine and apomorphine were comparable in the 6-OHDA and sham group. The rate-decreasing effects were not altered in either group for any of the drugs. Upon sacrifice, dopamine (DA) was found to be significantly depleted in the accumbens, caudate and rest of brain of the 6-OHDA group. Levels of norepinephrine and serotonin were unaltered. These data suggest that central DA-containing neurons play a role in the discriminative stimulus properties of psychomotor stimulants in rats.

Neurochemical and behavioural studies with RU-24969 in the rat.

The regional brain synthesis of serotonin (5-HT) and dopamine (DA) was studied in rats after various doses of 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU-24969), a 5-HT1 receptor agonist. The potential anxiolytic and antidepressant properties of the compound were examined as well. RU-24969 0.62 mg/kg significantly reduced 5-HT synthesis in the nucleus accumbens and hypothalamus, while with 1.25 and 2.5 mg/kg the effect was also seen in striatum, hippocampus, brainstem and cortex. RU-24969 2.5 and 5 mg/kg had no effect on DA synthesis in the striatum, while 5.0 mg/kg significantly increased it in the nucleus accumbens. At doses of 2.5 and 5.0 mg/kg the drug increased the motor activity of rats measured during 1 h in activity cages while 0.625 and 1.25 mg/kg had no effect. Doses ranging from 0.62 to 2.5 mg/kg RU-24969 significantly reduced unpunished responding in a test of conditioned suppression of drinking. Doses of 1.25 and 2.5 mg/kg also reduced punished responding. Finally, of various doses only 2.5 mg/kg RU-24969 significantly reduced the duration of immobility of rats in the forced swimming test but the effects were due to running around the cylinder rather than to escape attempts. In conclusion, RU-24969 reduced 5-HT synthesis in all brain areas examined, with a preferential effect for the nucleus accumbens and the hypothalamus. At higher doses, there was also a specific increase in DA synthesis in the nucleus accumbens. The compound raised the level of activity of rats but no clear evidence of any potential anxiolytic or antidepressant properties has been obtained.

Evidence of a preferential role of brain serotonin in the mechanisms leading to naloxone-precipitated compulsive jumping in morphine-dependent rats.

Various drugs acting on brain serotonin or catecholamines were administered concurrently with morphine during the development of dependence or before naloxone-precipitated withdrawal syndrome. Of the various drugs only cyproheptadine, a serotonin antagonist, and piribedil, a dopamine agonist, reduced the frequency of jumping (but not of diarrhea or ptosis) when administered with morphine during development of dependence. When administered before naloxone, d-fenfluramine, a serotonin releaser, markedly reduced jumping, but not diarrhea and ptosis, and clonidine blocked these latter signs without affecting the frequency of jumping. Of the other drugs examined only phenoxybenzamine reduced diarrhea in morphine-abstinent rats. It is suggested that serotonin is involved in the mechanisms which lead to compulsive jumping during naloxone-precipitated withdrawal, whereas adrenergic sites on which clonidine acts are mainly involved in the expression of signs, such as ptosis and diarrhea. No clear evidence was obtained of a role for dopamine in the withdrawal signs studied.

Antidepressant-like effect of neurotensin administered in the ventral tegmental area in the forced swimming test.

Locomotor activity and behaviour in the forced swimming test were examined in rats which had received neurotensin (0.5-5.0 micrograms) in the ventral tegmental area. Doses of 5 micrograms neurotensin but not lower increased the locomotor activity for at least 2 h. At 0.5 and 1.0 microgram neurotensin significantly increased the time the animals spent in struggling with no changes in general motor activity (swimming). The effect of 1.0 microgram neurotensin on struggling was completely antagonized by 0.5 microgram (-)-sulpiride administered in the posterior nucleus accumbens. The results suggest that activation of the mesolimbic dopamine system through administration of neurotensin in the ventral tegmental area produces antidepressant-like effects. The significance of these findings for a role of endogenous neurotensin in depression remains to be clarified.

Differences in the effects of d-fenfluramine and morphine on various responses of rats to painful stimuli.

The effects of d-fenfluramine and morphine on various nociceptive responses of rats were investigated. Unlike morphine, which inhibited all the responses examined, d-fenfluramine inhibited jumping and paw licking of rats on a hot plate, but did not increase the latency of tail withdrawal from hot water. The effects of d-fenfluramine on both responses on the hot plate were prevented by pretreatment with metergoline, a serotonin antagonist, whereas this pretreatment only reduced the effect of morphine on paw licking. The inhibition of tail withdrawal by morphine was also significantly reduced by metergoline treatment. The results confirm previous findings suggesting a role of serotonin in the mechanism by which morphine inhibits some nociceptive responses in rats. They also show that d-fenfluramine, a selective releaser and uptake inhibitor of serotonin at nerve endings, does not completely reproduce the antinociceptive effects of morphine in this species.

Autoradiographic localization of [(3)H]paroxetine specific binding in the rat brain.

Specific binding of [(3)H]paroxetine, a selective serotonin uptake inhibitor, has recently been described. We used the autoradiographic technique to establish the regional distribution of these binding sites in the brain of control and 5,7-dihydroxytryptamine (5,7-DHT) lesioned rats. Binding levels were highest in the dorsal raphe, followed by superior colliculus, thalamus, mammillary nuclei, ventral tegmental area and substantia nigra. Values were intermediate in hippocampus, hypothalamus, caudate nucleus and median raphe and lowest in the cerebral cortex and cerebellum. The degeneration of serotonergic terminals by 5,7-DHT completely prevented specific binding in the majority of brain regions analyzed, with the exceptions of raphe nuclei, ventral tegmental area and caudate nucleus. These data indicate that [(3)H]paroxetine binding sites are mainly localized on serotonin nerve terminals even if it seems that they cannot always be directly correlated to 5-HT uptake.

Effects of dopaminergic and glutamatergic receptor antagonists on the acquisition and expression of cocaine conditioning place preference.

A balanced conditioning place preference (CPP) paradigm was used to study the role of dopamine D1 and D2 and glutamatergic NMDA and AMPA/kainate receptors on the acquisition and expression of cocaine place conditioning. The D1 receptor antagonist SCH 23390 (0.1-0.2 mg/kg i.p.), administered before cocaine during the training phase, significantly blocked the establishment of place conditioning (acquisition) but had no effect when administered before testing for place preference in the absence of cocaine (expression). Similar results were obtained with the non-competitive NMDA receptor antagonist MK-801 (0.1-0.5 mg/kg i.p.). The D2 receptor antagonist (-)-sulpiride (50-100 mg/kg i.p.) had no effect on either acquisition or expression of cocaine CPP. The AMPA/kainate receptor antagonist DNQX, administered intracerebroventricularly (0.2-3 micrograms/10 microliters), blocked cocaine CPP when given before testing but not when given before cocaine during the training trials. The results suggest that dopaminergic D1 (but not D2) and glutamatergic NMDA receptors are involved in the primary rewarding properties of cocaine (as assessed by the establishment of CPP) whereas the AMPA/kainate receptors are important only for the behaviour elicited by the stimuli previously associated with the drug action (CPP expression). The implications for the treatment of cocaine craving and relapse are discussed.

Effects of dopaminergic and glutamatergic receptor antagonists on the establishment and expression of conditioned locomotion to cocaine in rats.

A series of experiments were conducted to investigate the role of dopaminergic D1 and D2 and glutamatergic NMDA and AMPA/kainate receptors on the establishment and expression of cocaine-induced conditioned locomotion in rats. In the first experiment conditioned locomotion was demonstrated by testing the animals in an environment previously associated with 15 mg/kg i.p. cocaine. The D2-receptor antagonist (-)-sulpiride (50 and 100 mg/kg i.p.) administered before cocaine during the conditioning phase did not modify the establishment of conditioned locomotion whereas when administered before testing only at the higher dose it partially reduced rats' locomotion in the absence of cocaine (expression). At the higher dose (0.1 mg/kg i.p.) the D1-receptor antagonist SCH 23390 attenuated the expression of cocaine-induced conditioned locomotion whereas the lower dose (0.03 mg/kg i.p.) had no effect. Both doses of the NMDA receptor antagonist MK-801 (0.125 and 0.25 mg/kg i.p.) blocked the development of cocaine-induced conditioned locomotion but neither dose, when administered before testing, modified locomotion in the absence of cocaine. Both doses of the AMPA/kainate receptor antagonist DNQX administered intracerebroventricularly (1 and 3 micrograms/rat) blocked cocaine-induced conditioned locomotion when given before cocaine during conditioning but when given before testing only the higher dose attenuated the conditioned activity. The results confirm the importance of the interaction between glutamatergic and dopaminergic systems for the conditional factors maintaining drug seeking behaviour. The findings may have implications for the treatment of cocaine craving and relapse.