Effect of chronic antipsychotic drug treatment on preprosomatostatin and preprotachykinin A mRNA levels in the medial prefrontal cortex, the nucleus accumbens and the caudate putamen of the rat

In situ hybridization histochemistry was used to study the expression of preprosomatostatin (PPSOM) and preprotachykinin A (PPT-A) mRNA in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAC) and the caudate putamen (CP) of the rat after chronic (21 days) treatment with the classical antipsychotic drug haloperidol (1 mg/kg i.p.), the atypical antipsychotic drugs clozapine (15 mg/kg i.p.) and amperozide (5 mg/kg i.p.), and the selective dopamine (DA)-D2/D3 receptor antagonist raclopride (2 mg/kg i.p.). Whereas amperozide markedly elevated the numerical density of PPSOM mRNA expressing neurons in the mPFC (52%), the other drugs did not significantly affect PPSOM mRNA levels in any of the brain regions studied. Amperozide also altered PPT-A mRNA expression in the mPFC, i.e. a decrease (22%) was found. Of the other drugs tested only haloperidol significantly decreased PPT-A mRNA levels in the NAC shell (14%), in the dorso-lateral CP (19%) and in the medial CP (15%). In view of the differences between amperozide and the other drugs studied, as regards both pre-clinical and clinical characteristics, we suggest that the specific effects of amperozide on PPSOM and PPT-A mRNA in the mPFC may be related to its 5-HT releasing action in the frontal cortex, an effect possibly caused by its alpha2-adrenoceptor blocking activity. This effect, in turn, may be related to an antidepressant-like action that this compound exhibits in animal studies. The decrease in PPT-A mRNA levels seen after the haloperidol treatment is probably due to its potent DA-D2 receptor antagonism and may be related to side-effects, rather than therapeutic effects of this drug.

Motor depressant effects mediated by dopamine D2 and adenosine A2A receptors in the nucleus accumbens and the caudate-putamen

We compared hypolocomotion and catalepsy mediated by striatal dopamine D2 and adenosine A2A receptors using microinfusions of the adenosine A2A receptor agonist 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS21680) and the dopamine D2 receptor antagonist raclopride into the nucleus accumbens and the caudate-putamen. The effective doses (ED25/50) of CGS21680 and raclopride which produced equivalent reductions of spontaneous locomotion after microinfusion into the nucleus accumbens were found to induce similar degrees of catalepsy after microinfusion into the caudate-putamen. This comparable, little separation of the effective doses of a dopamine D2 receptor antagonist and an adenosine A2A receptor agonist to produce locomotor inhibition and catalepsy support the idea that adenosine A2A receptor agonists as potential antipsychotic agents may have a similar therapeutic profile as dopamine D2 receptor antagonists.

The effects of chronic levodopa treatment on pre- and postsynaptic markers of dopaminergic function in striatum of parkinsonian monkeys

Therapeutic treatment of parkinsonian monkeys by chronic administration of levodopa (l-DOPA) leads to the development of dyskinesias and other motor fluctuations. It is unclear whether there are alterations in the dopamine system that are related to the induction of dyskinesias by l-DOPA, but recent attention has focused on the D1 receptor system. The present study assessed the consequences of chronic l-DOPA treatment in monkeys made parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on indices of the pre- and post-synaptic dopamine (DA) system. Treatment with therapeutic doses of l-DOPA led to the induction of dyskinesias in the MPTP-treated monkeys. High-pressure liquid chromatography was used for measurement of tissue levels of DA and its metabolites, and quantitative autoradiography was used to examine the regional integrity of the presynaptic DA system (by measuring [3H]mazindol binding to DA uptake sites). Quantitative autoradiography was used to measure the number of postsynaptic D1 receptors (using [3H] SCH 23390) in the striatum and pallidum of normal, MPTP alone, and MPTP monkeys treated chronically with l-DOPA. In both MPTP-treated monkeys, levels of DA and metabolites as well as [3H]mazindol binding were greatly reduced in the caudate and putamen, slightly more in dorsal than in ventral areas. However, the lack of increase in striatal DA levels along with higher [3H]mazindol binding in MPTP-plus-l-DOPA-treated monkeys suggested differences in the way DA was used after l-DOPA treatment In MPTP-treated monkeys, a significant increase (141-170% of normals) of D1 receptor numbers was observed in putamen and dorsal caudate. With l-DOPA treatment, the number of D1 receptor numbers was further elevated in caudal putamen (119-123%), dorsal caudate (110-130%), and in the internal segment of the globus pallidus (GPi; 164% of normals) of MPTP-treated monkeys as compared with MPTP treatment alone. This suggested that in MPTP-treated monkeys made dyskinetic by chronic pulsatile delivery of l-DOPA, there was enhanced production of D1 receptors in the direct striatal output to the GPi.

Positron emission tomography studies of healthy volunteers--no effects on the dopamine terminals and synthesis after short-term exposure to toluene

Despite extensive research, the mechanisms for the effects of organic solvents on the central nervous system are still unknown. One mechanism proposed is that solvents interfere with the synthesis of neurotransmitters. In the present study 11 male healthy volunteers were exposed during 15 min to 100 p.p.m. toluene at light physical exercise, and the dopamine decarboxylase activity and number of terminals in putamen were measured before and after exposure by positron emission tomography. Two different tracers were used [beta-11C]L-DOPA for decarboxylase activity during the in vivo synthesis of dopamine, and [11C]nomifensine to estimate the number of terminals. Although there was a slight increase in the rate of dopamine synthesis in the putamen after the exposure, this difference was not statistically significant (P = 0.4). No effect was observed with regard to the uptake of nomifensine. There was no significant relationship between the dose of toluene and rate of dopamine synthesis, and no significant correlation between the time from end of exposure to start of the PET-camera and DOPA. Our findings indicate that short term exposure to 100 p.p.m. of toluene does not affect the rate of dopamine synthesis or the number of presynaptic terminals.

Self-injurious behavior and dopaminergic neuron system in neonatal 6-hydroxydopamine-lesioned rat: 2. Intracerebral microinjection of dopamine agonists and antagonists

Intracisternal 6-hydroxydopamine treatment to newborn rats caused massive and permanent damage of brain dopaminergic neurons, and many of these animals show self-injurious behavior (SIB) when loaded by systemic injection of L-dihydroxyphenuylalanine (L-DOPA) or D1 agonist, SKF-38393. SIB occurred at life-long time in neonatal 6-hydroxydopamine-lesioned rats, because SIB confirmed rats at 4 to 6 wk all showed SIB at 3 to 5 mo and at 12 to 13 mo after L-DOPA loading. To elucidate the brain locus important for the induction and cessation of SIB, in our study, we microinjected dopamine agonists and antagonists into various dopamine neuron innervating areas. L-DOPA-induced SIB was inhibited by the injection of a D1 antagonist, SCH-23390 (5 microg), into the bilateral substantia nigra, but not into the bilateral caudate-putamen or nucleus accumbens. The microinjection of YM-09151-2 (10 microg), a D2 antagonist, into these regions could not stop SIB. For examining the important area for the induction of SIB, we microinjected SKF-38393, D1 agonist, and/or LY-141865, D2 agonist (each 1 microg) into bilateral (or ipsilateral) caudate-putamen and substantia nigra. SIB was induced only in the case of D1 and D2 receptors in both the bilateral caudate putamen and bilateral substantia nigra being stimulated simultaneously by the mixed application of SKF-38393 and LY-141865. SIB was not induced by the sole injection of SKF-38393 into bilateral caudate-putamen or bilateral substantia nigra. These observations suggest that both caudate-putamen and nigral D1- and D2-like receptors are important for the induction of SIB, but, for cessation of SIB, up-regulated nigral D1 receptor is crucial.

Dopamine agonist-induced inhibition of neurotransmitter release from the awake squirrel monkey putamen as measured by microdialysis

Male squirrel monkeys (Saimiri sciureus) were surgically prepared with cranial guide cannulae for acute microdialysis sampling of the putamen nucleus, a dopamine (DA)-rich brain region. On the day of an experiment an animal was placed in a Plexiglas restraining chair and a microdialysis probe was inserted through the guide into the putamen. Perfusates of artificial cerebrospinal fluid were collected every 20 min over several hours and analyzed via HPLC with electrochemical detection. DA D2/ D3 agonist drugs were administered either orally (p.o.) or subcutaneously (s.c.), and changes in levels of DA in the dialysates were measured. All of the drugs tested, i.e., quinpirole (0.5 mg/kg p.o.), talipexole (0.75 mg/kg p.o. or s.c.), and PD 135222 (7 mg/kg p.o.), decreased spontaneous DA overflow by approximately 40-50% during the first 2 h following dosing. In animals that routinely underwent the microdialysis procedure up to 23 times over a 2-year period, there was neither an appreciable change in basal DA overflow nor a significant change in the magnitude of drug response. These data suggest that DA D2/D3 agonists attenuate DA neuronal overflow in the primate brain, similar to effects seen in rodents. Furthermore, these results also demonstrate the utility of repeated intracerebral microdialysis as a tool to monitor dynamic changes in neurochemical activity in monkeys over a prolonged period of time.

Reduced eticlopride-induced Fos expression in caudate-putamen and globus pallidus after unilateral frontal cortex injury: relation to neglect

Unilateral ablation of medial agranular cortex in rats results in neglect of contralateral stimuli and reductions in amphetamine-induced expression of the immediate early gene, c-fos, in both caudate-putamen and globus pallidus. Both unilateral neglect and the reductions in dopamine agonist induction of subcortical Fos immunoreactivity dissipate over a matter of weeks. Dopamine agonism induces Fos predominantly in striatonigral cells and in globus pallidus via striatopallidal disinhibition, whereas Fos is induced in striatopallidal cells by administration of antagonists of the D2 dopamine receptor subfamily. To examine more directly effects of cortical injury on striatopallidal function, induction of striatal Fos by the D2 antagonist eticlopride (0.1 mg/kg, s.c.) was examined in rats with medial agranular cortex ablation. In the same animals, eticlopride-induced Fos in globus pallidus was also examined. Five days after unilateral cortex injury, in rats showing neglect, the numbers of Fos immunoreactive nuclei induced by eticlopride were reduced by 50% in caudate-putamen and 25% in globus pallidus of the ipsilateral hemisphere. These lesion effects were restricted to dorsolateral caudate-putamen and dorsal pallidum. Three or more weeks after cortical injury, in rats recovered from neglect, eticlopride-induced Fos was normalized in caudate-putamen, but still decreased by 20% in globus pallidus. Along with previous findings, these results suggest that behavioral recovery from neglect produced by cortical injury may be at least partially mediated by normalizations of function of both striatopallidal and striatonigral neurons. In addition, the present findings suggest that normalization of function of pallidal cells activated by eticlopride is not necessary for behavioral recovery from frontal cortex ablation. Lingering reductions in excitatory cortico-subthalamo-pallidal input may be responsible for the longer-lasting dysfunctions of these pallidal cells.

Long-term changes of striatal dopamine D2 receptors in patients with Parkinson's disease: a study with positron emission tomography and [11C]raclopride

We used [11C]raclopride (RACLO) and positron emission tomography (PET) to study longitudinally striatal dopamine D2 receptor binding in nine patients with Parkinson's disease (PD) at an early drug-naive stage and 3-5 years later, when motor fluctuations had appeared in seven of them. Patients were treated with a combination of levodopa and dopamine agonists. Data were compared with 10 healthy controls in the same age range. Initially, patients with PD showed a significant increase of RACLO uptake in the putamen compared with controls (p < 0.04). The caudate nucleus revealed values in the normal range. After 3-5 years, RACLO binding was significantly reduced in the putamen (p < 0.03) and caudate nucleus (p < 0.03) compared with baseline. Values were now in the control range in the putamen and reduced in the caudate nucleus (p < 0.05). The clinical score at "off" had significantly worsened (p < 0.0005) compared with the first PET scan. The nine PD patients reported here had already been investigated 3-4 months after therapy began and that time did not show a reduction of the initially increased RACLO binding capacity (data published previously). These results indicate long-term downregulation of striatal dopamine D2 receptor binding in PD. Receptor changes in the striatum of patients with PD may be induced by chronic dopaminergic therapy or occur independently of treatment, as a result of structural adaptation of the postsynaptic dopaminergic system to the progressive decline of nigrostriatal neurons.

Opposite role of delta 1- and delta 2-opioid receptors activated by endogenous or exogenous opioid agonists on the endogenous cholecystokinin system: further evidence for delta-opioid receptor heterogeneity

Using the mouse caudate-putamen, where delta-opioid receptor subtypes have been shown to regulate adenylyl cyclase activity, we show in this study that endogenous enkephalins inhibit enzyme activity through activation of delta 1- and delta 2-opioid receptors. Thus, naltriben or 7-benzylidenenaltrexone as well as the delta-selective antagonist naltrindole (mixed delta 1 and delta 2 antagonist) antagonized inhibition of adenylyl cyclase activity induced by methionine- or leucine-enkephalin, while the micro-antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) was without effect. Furthermore, we have previously shown that activation of delta-opioid receptors increases cholecystokinin release in the central nervous system, resulting in a potentiation of micro-opioid antinociceptive responses, and the respective role of delta 1- and delta 2-opioid receptors in this facilitatory effect has now been evaluated. Activation of delta 2-opioid receptors, either by endogenous enkephalins protected from catabolism by the complete enkephalin-degrading enzyme inhibitor N-((R,S)-2-benzyl-3((S)(2-amino-4-methyl-thio) butyldithio)-1-oxopropyl)-L-phenyl-alanine benzyl ester (RB 101), or by the delta 2-selective agonist Tyr-D-Ser(O-tert-butyl)-Gly-Phe-Leu-Thr(O-tert-butyl) (BUBU), potentiated micro-opioid antinociceptive responses in the hot-plate test in mice. This effect was antagonized by a selective cholecystokinin-A antagonist. Activation of delta 1-opioid receptors by endogenous opioid peptides decreased the micro-opioid responses. These results suggest that stimulation of delta 2-opioid receptors potentiates micro-opioid analgesia in the hot-plate test in mice through an increase in endogenous cholecystokinin release, while activation of delta 1-opioid receptors could decrease it. Thus, the pre-existing physiological balance between opioid and cholecystokinin systems seems to be modulated in opposite directions depending on whether delta 1- or delta 2-opioid receptors are selectively activated. This is the first demonstration that endogenous enkephalins, methionine- and leucine-enkephalin, are the natural ligands of delta-opioid receptor subtypes, and that delta 2-opioid receptor activation may facilitate the endogenous cholecystokinin-related modulation of micro-opioid analgesia, while the delta 1-opioid receptors may have an inhibitory role. These results could have important applications for the characterization of opioid delta 1 and delta 2 as subtypes or subsites and in pain alleviation.

Chronic clozapine versus chronic haloperidol treatment: differential effects on electrically evoked dopamine efflux in the rat caudate putamen, but not in the nucleus accumbens

Fast cyclic voltammetry at carbon-fibre micro-electrodes was used to investigate the effects of chronic clozapine or haloperidol administration on electrically evoked dopamine efflux in the nucleus accumbens and caudate putamen of the anaesthetized rat. Stimulation trains were delivered to the median forebrain bundle (60 pulses, 350 microns duration) every 5 min, and the evoked dopamine efflux measured as a function of a) the applied stimulus intensity (range 0.2 mA-1.0 mA), and b) the applied stimulus frequency (range 10 Hz-250 Hz). Chronic administration of either clozapine (20 mg/kg x 21 days, p.o.) or haloperidol (1 mg/kg x 21 days, p.o.) significantly reduced electrically evoked dopamine efflux in the nucleus accumbens over the range of stimulus intensities and frequencies tested. The reduction in evoked dopamine efflux observed in the nucleus accumbens of clozapine- and haloperidol-treated rats showed no statistically significant difference. In contrast, only chronic haloperidol treatment significantly reduced evoked dopamine efflux in the caudate putamen. These findings demonstrate that chronic treatment with either the atypical neuroleptic, clozapine, or the typical neuroleptic, haloperidol, produce long-term changes in mesolimbic dopamine function; actions which may underlie their antipsychotic efficacy. They also provide further evidence that the sparing action of clozapine on nigrostriatal dopamine activity may underlie the lower incidence of extrapyramidal side effects associated with its long-term administration.

Nitrogen-based drugs are not essential for blockade of monoamine transporters

In brain, monoamine transporters are principal targets of widely used therapeutic drugs including antidepressants, methylphenidate (Ritalin), and the addictive drug cocaine. Without exception, these transport blocking agents contain an amine nitrogen. A prevalent view and untested premise is that an amine nitrogen is needed to bind to the same counterion on the transporter as does the amine nitrogen of the monoamine neurotransmitter. We report that several compounds without nitrogen (8-oxa-bicyclo-3-aryl-[3.2.1] octanes, or aryloxatropanes) are active at monoamine transporters. One of these, tropoxane (0-914), bound with high affinity to the dopamine (IC50: 3.35 +/- 0.39 nM), serotonin (IC50: 6.52 +/- 2.05 nM), and norepinephrine (IC50: 20.0 +/- 0.3 nM) transporters in monkey brain, the human striatal dopamine transporter (IC50: 5.01 +/- 1.74 nM), and blocked dopamine transport (IC50: 7.2 +/- 3.0 nM) in COS-7 cells transfected with the human dopamine transporter. These unique compounds require a revision of current concepts of the drug binding domains on monoamine transporters, open avenues for discovery of a new generation of drugs and raise the issue of whether mammalian transporters and receptors may respond to, as yet, undiscovered non-amine bearing neurotransmitters or drugs.

Neurotensin, N-acetyl-aspartylglutamate and beta-endorphin modulate [3H]dopamine release from guinea pig nucleus accumbens, prefrontal cortex and caudate-putamen

Dopaminergic hyperactivity in nucleus accumbens and dopaminergic hypoactivity in prefrontal cortex are thought to underlie positive and negative symptoms of schizophrenia, respectively. The caudate putamen is the neuroanatomical substrate for extrapyramidal side effects resulting from chronic antipsychotic treatment. We sought to identify potential endogenous regulators of dopamine release that might produce differential effects in these brain areas. We tested neurotensin, N-acetyl-aspartyl-glutamate and beta-endorphin for potential regulation of [3H]dopamine release in these regions of guinea pig brain. All three peptides stimulated dopamine release, above basal activity, at all concentrations tested in the three regions. Neurotensin significantly enhanced and N-acetyl-aspartyl-glutamate had no significant effect on N-methyl-D-aspartate-stimulated release from all three regions. In contrast, beta-endorphin significantly inhibited N-methyl-D-aspartate-stimulated release in nucleus accumbens and caudate putamen. These results suggest that these neuropeptides may regulate endogenous dopamine release and therefore may be potential therapeutic targets for antipsychotic drug development.

alpha-Phenyl-N-tert-butyl nitrone attenuates methamphetamine-induced depletion of striatal dopamine without altering hyperthermia

Methamphetamine (MA) administration to adult rats (4 x 10 mg/kg s.c.) induces neurotoxicity predominately characterized by a persistent reduction of neostriatal dopamine (DA) content. Hyperthermia following MA administration potentiates the resulting DA depletion. DA-derived free radicals are postulated to be a mechanism through which MA-induced neurotoxicity is produced. The spin trapping agent PBN reacts with free radicals to form nitroxyl adducts, thereby preventing damaging free radical reactions with cellular substrates. MA with saline pretreatment (Sal-MA) reduced neostriatal DA by 55% (P < 0.01 vs. Sal-Sal). MA with PBN pretreatment (PBN-MA) at 36 or 60 mg/kg reduced neostriatal DA by 36 and 22%, respectively (P < 0.05 and P < 0.01 vs Sal-MA) indicating partial protection. PBN pretreatment did not alter MA-induced hyperthermia. Thus, PBN does not attenuate MA-induced neurotoxicity by reducing MA-induced hyperthermia. These results support a role for free radicals in the generation of MA-induced dopaminergic neurotoxicity.

Local administration of dopaminergic drugs into the ventral tegmental area modulates cataplexy in the narcoleptic canine

Cataplexy in the narcoleptic canine may be modulated by systemic administration of monoaminergic compounds. In the present study, we have investigated the effects of monoaminergic drugs on cataplexy in narcoleptic canines when perfused locally via microdialysis probes in the amygdala, globus pallidus/putamen, basal forebrain, pontine reticular formation and ventral tegmental area of narcoleptic and control Doberman pinchers. Cataplexy was quantified using the Food-Elicited Cataplexy Test and analyzed by electroencephalogram, electroculogram and electromyogram. Local perfusion with the monoaminergic agonist quinpirole, 7-OH-DPAT and BHT-920, into the ventral tegmental area produced a dose-dependent increase in cataplexy without significantly reducing basal muscle tone. Perfusion with the antagonist raclopride in the same structure produced a moderate reduction in cataplexy. Local perfusion with quinpirole, 7-OH-DPAT and BHT-920 into the globus pallidus/putamen also produced an increase, while raclopride produced a decrease, in cataplexy in narcoleptic canines. In control animals, none of the above drugs produced cataplexy or muscle atonia when perfused into either the ventral tegmental area or the globus pallidus/putamen. Other monoaminergic drugs tested in these two brain areas; prazosin, yohimbine, amphetamine, SKF 38393 and SCH 23390 had no effects on cataplexy. Local perfusion with each of the above listed drugs had no effect on cataplexy in any of the other brain regions examined. These findings show that cataplexy may be regulated by D2/D3 dopaminergic receptors in the ventral tegmental area and perhaps the globus pallidus/ putamen. It is suggested that neurons in the mesolimbic dopamine system of narcoleptics are hypersensitive to dopaminergic autoreceptor agonists.

Involvement of the caudal striatum in auditory processing: c-fos response to cortical application of picrotoxin and to auditory stimulation

The topographical organization of corticostriatal connections have been postulated to follow a longitudinal pattern, each cortical area projecting on a longitudinal strip stretching along the whole rostro-caudal axis of the striatum. However, compared to the rostral striatal region, the caudal striatum exhibits distinct features in terms of connectivity and neuronal phenotype. The induction of c-fos expression in the striatum by cortical activation or sensory stimulation may throw more light on these functional corticostriatal relationships. In the present study, we examined the effects of cortical activation by local application of picrotoxin on the Fos-immunoreactivity (Fos-IR) in the striatum of the mouse, with special reference to the caudal part of the striatum. Activation of the auditory cortex induced a dense ipsilateral Fos-IR restricted to the caudal striatum i.e., in the caudo-medial striatum and in the caudal part of fundus striati, and a very sparse labelling in the medial region of the rostral striatum. Conversely, activation of both sensori-motor and visual cortices only resulted in Fos-IR in the main rostral part of the striatum, without response in the caudal extremity of the striatum. On the other hand, visual or auditory stimulation in awake animals failed to induce c-fos expression in the striatum. However, using quantitative in-situ hybridization for c-fos mRNA, we found that auditory, but not visual stimulation significantly potentiated the c-fos response to the D1 agonist SKF 38393 (2 mg/kg, i.p.) in the caudal part of the striatum. These functional observations suggest that, despite a more widespread cortico-striatal connection pattern deduced from tracing experiments, the strongest functional projections from the auditory system mainly converge onto a restricted part of the caudal striatum, according to a connection pattern that is reminiscent of the transverse segmentation proposed in early lesioning studies of corticostriatal projections.

Suppression of K+ conductance by metabotropic glutamate receptor in acutely dissociated large cholinergic neurons of rat caudate putamen

1. Responses to metabotropic glutamate receptor (mGluR) activation were investigated in acutely dissociated rat neostriatal (caudate putamen, CP) large cholinergic neurons, with the use of a nystatin-perforated patch-clamp technique. 2. Application of L-glutamate (Glu) in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) induced a slow inward current accompanied by a decrease in membrane conductance at a holding potential (VH) of -44 mV. 3. The ratio of the maximal amplitude of the slow inward metabotropic glutamate (mGlu) response to that of the ionotropic glutamate response for large cholinergic CP neurons was larger than that for the hoppocampal CA1, CA3, and dentate gyrus neurons the nucleus tractus solitarii neuron, cerebellar Purkinje neuron, and granule cell of the main olfactory bulb. The threshold and half-maximal effective concentration values of these mGlu responses were 10- to 30-fold lower than those of the respective ionotropic responses. 4. Specific agonists of the mGluR, quisqualate (QA), (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (tACPD), (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD], and (2S,3S,4S)-alpha-carboxycyclopropyl-glycine [L-CCG-1), similarly induced slow inward currents at the same VH. The relative affinities of the mGlu agonists were QA > Glu > L-CCG-1 > (1S,3R)-ACPD. L-CCG-1 did not induce any current at concentrations < 10(-6) M. 5. DL-2-amino-3-phosphonopropionic acid or DL-2-amino-4-phosphonobutyric acid did not block the mGlu response, whereas (RS)-alpha-methyl-4-carboxyphenyl-glycine, a selective mGluR antagonist, partially reduced the mGlu response. 6. The reversal potential of the mGlu response was close to the K+ equilibrium potential, and it shifted by 56.4 mV for a 10-fold change in extracellular K+ concentration. In 90.6% of the neurons tested, the instantaneous current induced by hyperpolarizing voltage steps was markedly suppressed during the mGlu response. In 9.4% of the neurons, the currents elicited by step pulses showed a voltage-dependent slow relaxation that was not affected by mGluR activation. 7. Under the current-clamp mode, the slow afterhyperpolarization (AHP) following a spontaneous discharge was not affected by tACPD. The AHP current was not blocked under the voltage-clamp mode, either. 8. (1S,3R)-ACPD or Glu in the presence of CNQX elicited membrane depolarization accompanied by increased rate of action potentials under the current-clamp mode. Tetrodotoxin had no effect on the membrane depolarization. 9. These results indicate that the mGluR on large cholinergic CP neurons is mainly of the mGluR1 and/or mGluR5 type, and it plays a significant role in controlling the membrane potential by way of suppressing the leak K+ conductance.

Chronic intracerebroventricular cocaine differentially affects prodynorphin gene expression in rat hypothalamus and caudate-putamen

We investigated the effects of sustained administration of cocaine on the regulation of prodynorphin gene expression in rat brain. Intracerebroventricular (i.c.v.) infusion of cocaine hydrochloride (30 micrograms/day) for 7 days, by means of osmotic minipumps, elicited a significant 35% decrease of prodynorphin mRNA levels in rat hypothalamus and increase (22%) in caudate-putamen. At the same time and in the same animals, no significant changes were detected in the hippocampus or in the nucleus accumbens. These results indicate that continuously infused cocaine is able to modulate expression of the prodynorphin gene in opposite directions or has no effect on prodynorphin expression, depending on the brain region analysed. Cocaine, as well as opiates, might activate specific neuronal pathways, shared by different classes of drugs of abuse, involving, at least in part, the endogenous opioid system.

The effects of N-methyl-D-aspartate (NMDA) and its competitive antagonist, 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP), injected into caudate-putamen on kindled amygdaloid seizures in rats

N-methyl-D-aspartate (NMDA) is an agonist of NMDA receptors and 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP) is an NMDA receptor antagonist. NMDA (1 or 2 nmol per side) or CPP (2.5 or 10 nmol per side) was injected into the bilateral caudate-putamen of amygdaloid-kindled rats. In addition, CPP (10 nmol) was ipsilaterally or contralaterally injected into the unilateral caudate-putamen. Either 20 min after NMDA or 60 min after CPP, the kindled amygdala was stimulated at the generalized seizure triggering threshold. In a few animals tested, injection of NMDA into the bilateral caudate-putamen produced transient spiking activity, with no clinical manifestations. This feature began about 5 min after the injection and lasted about 10 s. When these animals were excluded from the statistical analysis, NMDA in the caudate-putamen showed a weak and non-significant anticonvulsant action. Injection of CPP into the bilateral caudate-putamen caused no ictal change, but markedly suppressed the kindled seizures. Injection of CPP into the unilateral caudate-putamen, regardless of the site, did not cause any ictal change, or affect the stimulation of the amygdala. These findings suggest that: (1) NMDA receptors in the caudate-putamen facilitate the development of kindled amygdaloid seizures; (2) activation of NMDA receptors in the bilateral, but not in the unilateral, caudate-putamen is required for the generalization and expression of kindled amygdaloid seizures.

L-DOPA regulates glutamate decarboxylases mRNA levels in MPTP-treated monkeys

The effect of dopaminergic denervation, alone or followed by chronic intermittent L-DOPA administration, on the levels of mRNAs encoding for the two isoforms of the GABA-synthesizing enzyme, glutamate decarboxylase (GAD65 and GAD67), were measured by in-situ hybridization in the caudate and putamen of macaque monkeys. When compared to control monkeys, the level of GAD67 mRNA was increased in the putamen and caudate of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. On the other hand, GAD65 mRNA labeling in MPTP-treated monkeys was not significantly different from the controls. In MPTP-treated monkeys that received L-DOPA, a significant increase in both GAD67 and GAD65 mRNA levels was measured in the putamen when compared to control or MPTP-treated monkeys. The results suggest that the dyskinetic effect of L-DOPA is paralleled by an increased GABAergic activity in the striatum.

Effect of acute and chronic fluoxetine on extracellular dopamine levels in the caudate-putamen and nucleus accumbens of rat

Recent studies indicate that an increase in serotonergic (5-HT) activity in the nucleus accumbens (NAc) produces an increase in dopamine (DA) release, providing a possible mechanism for the involvement of DA in the therapeutic action of selective serotonin reuptake inhibitor (SSRI) antidepressants. However, acutely administered fluoxetine (2.5, 5.0, or 10.0 mg/kg, i.p.) failed to elevate extracellular levels of DA, or its metabolites in the NAc or caudate-putamen (CP). In fact, the highest dose produced a small (20%) decrease in DA levels in the NAc. Extracellular levels of the 5-HT metabolite 5HIAA were consistently decreased at all doses of fluoxetine in both structures. Since SSRIs generally require several weeks of treatment to be effective clinically, a second experiment examined the effect of chronic administration of fluoxetine. Chronic (21 day) daily treatment with 5 mg/kg had no effect on NAc basal levels of DA, DA metabolites, or 5HIAA, relative to a saline-treated control group. Finally, pretreatment with fluoxetine appeared to slightly enhance the elevation of NAc DA induced by an injection of cocaine (10 mg/kg, i.p.), an effect that was not quite significant (P < .06). In conclusion, the 5-HT-induced facilitation of NAc DA neurotransmission described in the literature may not be relevant to the therapeutic action of fluoxetine.

Effects of D2 dopamine receptor antagonists on Fos protein expression in the striatal complex and entorhinal cortex of the nonhuman primate

Recent studies have reported that acute administration of dopamine D2 receptor antagonists increases expression of the immediate early gene c-fos in the rat striatal complex. There have been no corresponding studies of the effects of D2 antagonists in primate species. Since all clinically effective antipsychotic drugs share D2 receptor antagonism, it is important to define the extent to which these drugs may alter expression of c-fos or its protein product, Fos, in primates. We therefore examined the effects of administration of two D2 receptor antagonists, haloperidol and metoclopramide, on Fos expression in the striatum and temporal cortices of the vervet monkey. Metoclopramide does not appear to possess significant antipsychotic efficacy but potently produces extra-pyramidal side effects, while haloperidol is an effective antipsychotic drug that produces extrapyramidal side effects. Both drugs increased the number of Fos-like immunoreactive (Fos-li) neurons in the caudate nucleus and putamen; the numbers of Fos-li neurons in these regions were increased in both the patch and matrix compartments. Haloperidol but not metoclopramide increased the number of Fos-li neurons in the nucleus accumbens shell. Similarly, haloperidol but not metoclopramide increased the number of Fos-li neurons in the entorhinal cortex. Neither drug altered Fos expression in the inferior temporal cortex. These data suggest that the dorsolateral caudate nucleus and putamen may be sites at which D2 receptor antagonists elicit extrapyramidal side effects, and the nucleus accumbens shell and entorhinal cortex may be loci at which the therapeutic actions of antipsychotic drugs are manifested.

Dyskinesias and tolerance induced by chronic treatment with a D1 agonist administered in pulsatile or continuous mode do not correlate with changes of putaminal D1 receptors in drug-naive MPTP monkeys

Nine monkeys (Macaca fascicularis) were rendered parkinsonian after intravenous administration of the toxin MPTP. Three of these animals received pulsatile administration of the D1 receptor agonist SKF 82958 (1 mg/kg, three times daily) while three were treated by continuous infusion via an osmotic mini-pump with SKF 82958 (at an equivalent amount daily) for 29 days. Untreated MPTP as well as healthy control animals were also studied. Relief of parkinsonian symptoms was observed in the three animals of the pulsatile group. However, dyskinesia occurred in two monkeys which had striatal dopamine depletion of > 99% compared to the non-dyskinetic animal slightly less denervated (94%). Monkeys receiving continuous SKF 82958 showed no anti-parkinsonian effect and no dyskinesia. All monkeys from the pulsatile and continuous group had measurable amount of plasma SKF 82958 as assayed by HPLC with electrochemical detection. In the putamen of all SKF 82958-treated monkeys, Bmax of D1 receptors labeled with [3H]SCH 23390 were increased versus untreated MPTP-monkeys with no change in Kd. In contrast, a decrease D1 receptor density was observed in the nucleus accumbens of untreated MPTP monkeys versus controls and this was not corrected with either pulsatile or continuous SKF 82958 treatments. D2 receptor density measured with [3H]spiperone binding was increased in the posterior putamen of SKF 82958-treated monkeys whereas no change was observed in the accumbens compared to control animals. Hence, tolerance with the continuous administration of a D1 agonist is not associated with a decrease of putaminal D1 or D2 receptor densities and dyskinesia could not be specifically associated with an increase of putaminal D1 receptors.

Regulation of kappa opioid receptor mRNA in the rat brain by "binge' pattern cocaine administration and correlation with preprodynorphin mRNA

We previously reported that 'binge' pattern administration of cocaine elevates preprodynorphin (ppDyn) mRNA in the caudate-putamen of rats. The present study confirms this finding. In addition, we report here that "binge' pattern administration of cocaine leads to a significant decrease in the mean level of kappa opioid receptor (KOR) mRNA in the substantia nigra, with no significant change in the mean level of KOR mRNA in the caudate-putamen. The decrease in KOR mRNA in the substantia nigra after 3 day or 14 day 'binge' administration of cocaine was comparable to the increase in ppDyn mRNA in the caudate-putamen. While there was no significant change in the mean levels of KOR mRNA in the caudate-putamen following cocaine administration, there was a positive within animal correlation between the levels of ppDyn mRNA and KOR mRNA in the caudate-putamen, both in animals administered saline and in animals receiving 'binge' cocaine for 14 days. Finally, mean levels of ppDyn or KOR mRNA in cocaine treated rats were not different from saline treated controls following a 10 day withdrawal from 14 days of 'binge' cocaine administration. The results provide evidence of regulation of KOR mRNA by cocaine in the substantia nigra.

Subchronic administration of clozapine, but not haloperidol or metoclopramide, decreases dopamine D2 receptor messenger RNA levels in the nucleus accumbens and caudate-putamen in rats

The effects of unique profile antipsychotic drugs on dopamine D2 receptors and D2 receptor messenger RNA were assessed following subchronic administration in rats. Male, Sprague-Dawley rats were administered oral haloperidol, clozapine, metoclopramide or no drug for three weeks via their drinking water. Tissue from the medial nucleus accumbens and dorsolateral caudate-putamen was dissected and analyzed by Northern blot analysis for levels of dopamine D2 receptor messenger RNA and binding assays conducted with [3H]spiperone for dopamine D2 receptors. Haloperidol and metoclopramide, but not clozapine, significantly increased [3H]spiperone in the caudate-putamen, but not the nucleus accumbens. Clozapine significantly decreased D2 messenger RNA levels in the caudate-putamen and the nucleus accumbens, while metoclopramide and haloperidol had no significant effect in either brain region. The finding of decreased D2 receptor messenger RNA levels produced by subchronic clozapine may account for the lack of striatal D2 receptor up-regulation, which was robustly observed after subchronic haloperidol and metoclopramide. Furthermore, since haloperidol and metoclopramide have a high liability for motor side effects, the current results relate favorably to the low motor side effect profile of clozapine.

Imidazoline binding sites in Huntington's and Parkinson's disease putamen

Binding of [3H]2-(2-benzofuranyl)-2-imidazoline ([3H]BFI) to the imidazoline I2 receptor was determined in putamen taken post mortem from patients with two extrapyramidal motor disorders, Parkinson's and Huntington's diseases, and age-matched control subjects. No deficit of binding was apparent in Parkinson's disease, indicating that the receptors are not present on nigrostriatal terminals. A significant loss (by 56%) in imidazoline I2 receptor binding was observed in Huntington's disease, consistent with the receptors being sited on degenerating neurons.