The role of metabotropic glutamate receptors in regulation of striatal proenkephalin expression: implications for the therapy of Parkinson's disease

Overactivity of the striatopallidal pathway, associated with an enhancement of enkephalin expression, has been suggested to contribute to the development of parkinsonian symptoms. The aim of the present study was to examine whether the blockade of group I metabotropic glutamate receptors: subtypes 1 and 5 (mGluR1/5), or stimulation of group II: subtypes 2 and 3 (mGluR2/3) may normalize enkephalin expression in the striatopallidal pathway in an animal model of parkinsonism. The proenkephalin mRNA level measured by in situ hybridization in the striatum was increased by pretreatments with haloperidol (1.5 mg/kg s.c., three times, 3 h apart). Triple (3 h apart), bilateral, intrastriatal administration of selective antagonists of mGluR1: (S)-(+)-alpha-amino-4-carboxy-2-methylbenzeneacetic acid (3 x 5 microg/0.5 microl) or 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate (3 x 2.5 microg/0.5 microl), reversed the haloperidol-induced increases in proenkephalin mRNA levels in the rostral and central regions of the striatum. Similarly, repeated (6 times, 1.5 h apart), systemic injections of an antagonist of mGluR5, 2-methyl-6-(phenylethynyl)pyridine (6 x 10 mg/kg i.p.) counteracted an increase in the striatal proenkephalin mRNA expression elicited by haloperidol. None of the abovementioned antagonists of mGluR1 and mGluR5 per se influenced the proenkephalin expression. Differential effects were induced by agonists of the group II mGluRs, viz. (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine administered intraventricularly (3 times at 0.1-0.2 microg/4 microl, 3 h apart) increased both the normal and haloperidol-increased proenkephalin mRNA level, whereas (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate injected intrastriatally (3 times at 15 microg/0.5 microl, 3 h apart) was ineffective. The present study indicates that the blockade of striatal glutamate receptors belonging to the group I (mGluR1 and mGluR5) but not stimulation of the group II mGluRs may normalize the function of the striatopallidal pathway in an animal model of parkinsonism, which may be important for future antiparkinsonian therapy in humans.     

The influence of group III metabotropic glutamate receptor stimulation by (1S,3R,4S)-1-aminocyclo-pentane-1,3,4-tricarboxylic acid on the parkinsonian-like akinesia and striatal proenkephalin and prodynorphin mRNA expression in rats

Group III metabotropic glutamate receptors (mGluRs) are widely distributed in the basal ganglia, especially on the terminals of pathways which seem to be overactive in Parkinson's disease. The aim of the present study was to determine whether (1S,3R,4S)-1-aminocyclo-pentane-1,3,4-tricarboxylic acid (ACPT-1), an agonist of group III mGluRs, injected bilaterally into the globus pallidus (GP), striatum or substantia nigra pars reticulata (SNr), can attenuate the haloperidol-induced catalepsy in rats, and whether that effect was related to modulation of proenkephalin (PENK) or prodynorphin (PDYN) mRNA expression in the striatum. Administration of ACPT-1 (0.05-1.6 microg/0.5 microl/side) caused a dose-and-structure-dependent decrease in the haloperidol (0.5 mg/kg i.p. or 1.5 mg/kg s.c.)-induced catalepsy whose order was as follows: GP>striatum>SNr. ACPT-1, given alone to any of those structures, induced no catalepsy in rats. Haloperidol (3 x 1.5 mg/kg s.c.) significantly increased PENK mRNA expression in the striatum, while PDYN mRNA levels were not affected by that treatment. ACPT-1 (3 x 1.6 microg/0.5 microl/side) injected into the striatum significantly attenuated the haloperidol-increased PENK mRNA expression, whereas administration of that compound into the GP or SNr did not influence the haloperidol-increased striatal PENK mRNA levels. Our results demonstrate that stimulation of group III mGluRs in the striatum, GP or SNr exerts antiparkinsonian-like effects in rats. The anticataleptic effect of intrastriatally injected ACPT-1 seems to correlate with diminished striatal PENK mRNA expression. However, since the anticataleptic effect produced by intrapallidal and intranigral injection of ACPT-1 is not related to a simultaneous decrease in striatal PENK mRNA levels, it is likely that a decrease in enkephalin biosynthesis is not a necessary condition to obtain an antiparkinsonian effect.     

Effects of intra-vestibular nucleus injection of the Group I metabotropic glutamate receptor antagonist AIDA on vestibular compensation in guinea pigs

Removal of the peripheral vestibular receptor cells in one inner ear (unilateral vestibular deafferentation, UVD) results in a syndrome of ocular motor and postural disorders, many of which disappear over time in a process of behavioural recovery known as vestibular compensation. Excitatory amino acid receptors, in particular the N-methyl-D-aspartate (NMDA) receptor, have been implicated in vestibular compensation; however, the metabotropic glutamate receptors (mGluRs) have not been studied in this context. The aim of this study was to determine whether group I mGluRs in the brainstem vestibular nucleus complex (VNC) ipsilateral to the UVD are involved in vestibular compensation of the static symptoms of UVD in guinea pig. The selective group I mGluR antagonist (RS)-1-aminoindan-1,5,dicarboxylic acid (AIDA) was continuously infused into the ipsilateral VNC for 30-min pre-UVD and 30-min post-UVD by cannula, at a rate of 1 microl/h, using one of four doses: 0.1 fg, 0.1 pg, 0.1 ng or 0.1 microg (n=5 animals in each case). In control conditions, a 0.1-fg (n=4) or 0.1-microg (n=5) NaOH vehicle was infused into the ipsilateral VNC using the same protocol. In order to control for the possibility that AIDA disrupted spontaneous neuronal activity in the VNC in normal animals, 0.1 microg AIDA (n=4) or 0.1 microg NaOH (n=2) was infused into the VNC in labyrinthine-intact animals. In both groups, static symptoms of UVD (i.e. spontaneous nystagmus, SN, yaw head tilt, YHT and roll head tilt, RHT) were measured at 8, 10, 12, 15, 20, 25, 30, 35, 45 and 50 h post-UVD. In addition, the righting reflex latency (RRL) was measured in labyrinthine-intact animals in order to assess whether AIDA impaired motor coordination in labyrinthine-intact animals. In UVD animals, the highest dose of AIDA significantly reduced SN frequency and changed its rate of compensation (P<0.001 and P<0.0001, respectively). This dose of AIDA also caused a significant reduction in YHT (P<0.005) as well as a significant change in its rate of compensation (P<0.0001). However, RHT was not significantly affected. In the labyrinthine-intact animals, AIDA infusion did not induce a UVD syndrome, nor did it significantly affect RRL. These results suggest that group I mGluRs in the ipsilateral VNC may be involved in the expression of ocular motor and some postural symptoms following UVD. Furthermore, group I mGluRs may not contribute to the resting activity of vestibular nucleus neurons.     

Antiparkinsonian properties of a nerve growth factor dipeptide mimetic GK-2 in in vivo experiments

An intraperitoneal injection of GK-2 (dipeptide mimetic of nerve growth factor, 0.01-5.00 mg/kg) 24 h before the adverse exposure reduced the severity of haloperidol-induced catalepsy in rats. This agent retained the activity after oral administration in a dose of 10 mg/kg. An intraperitoneal injection of GK-2 in a dose of 1 mg/kg reduced the severity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian syndrome in mice. Administration of GK-2 45 min after haloperidol treatment was also followed by a decrease in the degree of catalepsy. The repeated intraperitoneal treatment with GK-2 in a dose of 1 mg/kg after intrastriatal injection of 6-hydroxydopamine was shown to prevent the development of apomorphine- induced rotations in rats.     

Therapeutic potential of α2 adrenoceptor antagonism for antipsychotic-induced extrapyramidal motor disorders

We examined the effects of JP-1302 (a selective α_2C antagonist), BRL-44408 (a selective α_2A antagonist) and yohimbine (a non-selective α₂ antagonist) on haloperidol-induced bradykinesia and catalepsy in mice to elucidate the role of α₂ adrenoceptor subtypes in modifying extrapyramidal motor disorders. JP-1302 (0.1–1 mg/kg, s.c.) dose-dependently ameliorated haloperidol-induced bradykinesia in the pole-test and reversed the catalepsy time increased by haloperidol. Antibradykinetic and anticataleptic actions of JP-1302 were statistically significant at 0.3 and 1 mg/kg, and these doses did not alter the ambulatory distance, rearing or center–perimeter residence time in the open-field test. BRL-44408 (1–10 mg/kg, s.c.) and yohimbine (0.3–3 mg/kg, i.p.) also ameliorated haloperidol-induced bradykinesia and catalepsy. However, both agents significantly decreased ambulatory distance and rearing in the open-field test, possibly reflecting their anxiogenic actions associated with α_2A antagonism. The present study shows for the first time that blockade of α_2C receptors can alleviate antipsychotic-induced extrapyramidal motor disorders without affecting gross behaviors.     

Contribution of vesicular and cytosolic dopamine to the increased striatal dopamine efflux elicited by intrastriatal injection of dexamphetamine

Systemic administration of high doses of dexamphetamine induces a dopamine efflux that has its intracellular origin in both the vesicular, reserpine-sensitive dopamine pool and the cytosolic, alpha-methyl-para-tyrosine-sensitive, newly synthesized dopamine pool. It remains unknown whether locally administered dexamphetamine produces similar effects. Using a brain microdialysis technique that is combined with a microinjection needle, the contribution of the vesicular and cytosolic pools to the dopamine efflux induced by striatal injection of dexamphetamine was analyzed in rats. The transient striatal dopamine efflux induced by intrastriatal injection of dexamphetamine (1.0 microg/0.5 microl) was significantly reduced by systemic administration of reserpine (5mg/kg i.p., given 24 h earlier) or alpha-methyl-para-tyrosine (250 mg/kg i.p., given 2 h earlier). The effects of dexamphetamine on the striatal dopamine were nearly nullified by combined treatment with reserpine and alpha-methyl-para-tyrosine. The sum of the amounts of extracellular dopamine that was sensitive to either reserpine or alpha-methyl-para-tyrosine, was far greater than 100%, namely 146.1% of the basal dopamine level and 144.0% of the dexamphetamine-induced dopamine level. The present study indicates that both the vesicular dopamine pool and the cytosolic dopamine pool contribute to the transient increase of striatal dopamine efflux induced by intrastriatal injection of dexamphetamine. This study also suggests that striatally applied dexamphetamine can promote the redistribution of rat striatal dopamine from vesicles to the cytosol in vivo.     

Role of metabotropic glutamate receptor subtype mGluR1 in brief nociception and central sensitization of primate STT cells.

G-protein coupled metabotropic glutamate receptors (mGluRs) are important modulators of synaptic transmission in the mammalian CNS and have been implicated in various forms of neuroplasticity and nervous system disorders. Increasing evidence also suggests an involvement of mGluRs in nociception and pain behavior although the contribution of individual mGluR subtypes is not yet clear. Subtypes mGluR1 and mGluR5 are classified as group I mGluRs and share the ability to stimulate phosphoinositide hydrolysis and activate protein kinase C. The present study examined the role of group I mGluRs in nociceptive processing and capsaicin-induced central sensitization of primate spinothalamic tract (STT) cells in vivo. In 10 anesthetized male monkeys (Macaca fascicularis) extracellular recordings were made from 20 STT cells in the lumbar dorsal horn. Responses to brief (15 s) cutaneous stimuli of innocuous (BRUSH) and barely and substantially noxious (PRESS and PINCH, respectively) intensity were recorded before, during, and after the infusion of group I mGluR agonists and antagonists into the dorsal horn by microdialysis. Cumulative concentration-response relationships were obtained by applying different concentrations for at least 20 min each (at 5 microl/min). The actual concentrations reached in the tissue are 2-3 orders of magnitude lower than those in the microdialysis fibers (values in this paper refer to the latter). The group I antagonists were also applied at 10-25 min after capsaicin injection. S-DHPG, a group I agonist at both mGluR1 and mGluR5, potentiated the responses to innocuous and noxious stimuli (BRUSH > PRESS > PINCH) at low concentrations (10-100 microM; n = 5) but had inhibitory effects at higher concentrations (1-10 mM; n = 5). The mGluR5 agonist CHPG (1 microM-100 mM; n = 5) did not potentiate but inhibited all responses (10-100 mM; n = 5). AIDA (1 microM-100 mM), a mGluR1-selective antagonist, dose-dependently depressed the responses to PINCH and PRESS but not to BRUSH (n = 6). The group I (mGluR1 > mGluR5) antagonist CPCCOEt (1 microM-100 mM) had similar effects (n = 6). Intradermal injections of capsaicin sensitized the STT cells to cutaneous mechanical stimuli. The enhancement of the responses by capsaicin resembled the potentiation by the group I mGluR agonist S-DHPG (BRUSH > PRESS > PINCH). CPCCOEt (1 mM) reversed the capsaicin-induced sensitization when given as posttreatment (n = 5). After washout of CPCCOEt, the sensitization resumed. Similarly, AIDA (1 mM; n = 7) reversed the capsaicin-induced sensitization and also blocked the potentiation by S-DHPG (n = 5). These data suggest that the mGluR1 subtype is activated endogenously during brief high-intensity cutaneous stimuli (PRESS, PINCH) and is critically involved in capsaicin-induced central sensitization.     

Amygdaloid N-methyl-D-aspartate and gamma-aminobutyric acid(A) receptors regulate sensorimotor gating in a dopamine-dependent way in rats

Sensorimotor gating can be measured as prepulse inhibition of the startle response in humans and rats. Since prepulse inhibition is impaired in schizophrenics there is considerable interest in understanding the neuronal basis of prepulse inhibition. Neuropathological findings indicate a dysfunction of the glutamatergic and GABAergic system in cortico-limbic areas in schizophrenics. We tested whether blockade of N-methyl-D-aspartate or GABA(A) receptors in the basolateral amygdala affects prepulse inhibition in rats. Local infusion of the N-methyl-D-aspartate receptor antagonist dizocilpine (0, 6.25 microg/0.5 microl), or of the GABA(A) receptor antagonist picrotoxin (0, 5.0, 10.0 ng/0.5 microl) reduced prepulse inhibition. The prepulse inhibition-disrupting effect of 6.25 microg dizocilpine or 10.0 ng picrotoxin was reversed by systemic co-administration of the dopamine antagonist haloperidol (0.1mg/kg i.p.).These data indicate that sensorimotor gating is regulated in a dopamine-dependent way by N-methyl-D-aspartate and GABA(A) receptors in the basolateral amygdala. Our findings are discussed with respect to neuropathological findings in schizophrenics.     

Effects of calcitonin on the brain of aged rats

We have recently demonstrated that calcitonin, a putative neuromodulator, may influence extrapyramidal motor system by decreasing nigro-striatal dopaminergic function. Since calcitonin is extensively used in aged patients, we have investigated whether calcitonin might influence extrapyramidal motor behavior (haloperidol-induced catalepsy and apomorphine-induced hyperactivity) in rats of different ages. Intracerebroventricular injection of salmon calcitonin (I μg/kg) prevented apomorphine-induced hyperactivity in 2, 7, 18 or 21 month old rats, but potentiated haloperidol-induced catalepsy only in 2 or 7 month old rats. In addition, in all the animals salmon calcitonin significantly decreased the secretion of prolactin, an anterior pituitary hormone that may act at central level enhancing nigro-striatal dopaminergic activity.     

Baseline glutamate levels affect group I and II mGluRs in layer V pyramidal neurons of rat sensorimotor cortex

Possible functional roles for glutamate that is detectable at low concentrations in the extracellular space of intact brain and brain slices have not been explored. To determine whether this endogenous glutamate acts on metabotropic glutamate receptors (mGluRs), we obtained whole cell recordings from layer V pyramidal neurons of rat sensorimotor cortical slices. Blockade of mGluRs with (+)-alpha-amino-4-carboxy-alpha-methyl-benzeacetic acid (MCPG, a general mGluR antagonist) increased the mean amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), an effect attributable to a selective increase in the occurrence of large amplitude sEPSCs. 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495, a group II antagonist) increased, but R(-)-1-amino-2,3-dihydro-1H-indene-1,5-dicarboxylic acid (AIDA) and (RS)-hexyl-HIBO (group I antagonists) decreased sEPSC amplitude, and (R,S)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, a group III antagonist) did not change it. The change in sEPSCs elicited by MCPG, AIDA, and LY341495 was absent in tetrodotoxin, suggesting that it was action potential-dependent. The increase in sEPSCs persisted in GABA receptor antagonists, indicating that it was not due to effects on inhibitory interneurons. AIDA and (S)-3,5-dihydroxyphenylglycine (DHPG, a group I agonist) elicited positive and negative shifts in holding current, respectively. LY341495 and (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV, a group II agonist) elicited negative and positive shifts in holding current, respectively. The AIDA and LY341495 elicited currents persisted in TTX. Finally, in current clamp, LY341495 depolarized cells by approximately 2 mV and increased the number of action potentials to a given depolarizing current pulse. Thus ambient levels of glutamate tonically activate mGluRs and regulate cortical excitability.     

The role of kainic acid/AMPA and metabotropic glutamate receptors in the regulation of opioid mRNA expression and the onset of pain-related behavior following excitotoxic spinal cord injury.

Intraspinal injection of quisqualic acid, a mixed kainic acid/2-amino-3(3-hydroxy-5-methylisoxazol-4-yl)propionic acid and metabotropic glutamate receptor agonist, produces an excitotoxic injury that leads to the onset of both spontaneous and evoked pain behavior as well as changes in spinal and cortical expression of opioid peptide mRNA, preprodynorphin and preproenkephalin. What characteristics of the quisqualic acid-induced injury are attributable to activation of each receptor subtype is unknown. This study attempted to define the role of activation of the kainic acid/2-amino-3(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) and metabotropic glutamate receptor subtypes in the regulation of opioid peptide expression and the onset of spontaneous and evoked pain-related behavior following excitotoxic spinal cord injury by comparing quisqualic acid-induced changes with those created by co-injection of quisqualic acid and the kainic acid/AMPA antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline, (NBQX) or the metabotropic antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA). Therefore, 42 male Long-Evans adult rats were divided into seven treatment groups and received intraspinal microinjections of saline (sham), 0.5% dimethylsulphoxide (sham), quisqualic acid (1.2 microl, 125 mM), NBQX (1.2 microl, 60 microM), AIDA (1.2 microl, 250 microM), quisqualic acid/NBQX (1.2 microl, 125 mM/60 microM), or quisqualic acid/AIDA (1.2 microl, 125 mM/250 microM) directed at spinal levels thoracic 12-lumbar 2. Behavioral observations of spontaneous and evoked pain responses were completed following surgery. After a 10-day survival period, animals were killed and brain and spinal cord tissues were removed and processed for histologic analysis and in situ hybridization. Both AIDA and NBQX affected the quisqualic acid-induced total lesion volume but only AIDA caused a decrease in the percent tissue damage at the lesion epicenter. Preprodynorphin and preproenkephalin expression is increased in both spinal and cortical areas in quisqualic acid-injected animals versus sham-, NBQX or AIDA-injected animals. NBQX did not affect quisqualic acid-induced spinal or cortical expression of preprodynorphin or preproenkephalin except for a significant decrease in preproenkephalin expression in the spinal cord. In contrast, AIDA significantly decreases quisqualic acid-induced preprodynorphin and preproenkephalin expression within the spinal cord and cortex. AIDA, but not NBQX, significantly reduced the frequency of, and delayed the onset of, quisqualic acid-induced spontaneous pain-related behavior.From these data we suggest that both the kainic acid/AMPA and metabotropic glutamate receptor subtypes are involved in the induction of the excitotoxic cascade responsible for quisqualic acid-induced neuronal damage and changes in opioid peptide mRNA expression, while metabotropic glutamate receptors may play a more significant role in the onset of post-injury pain-related behavior.     

Behavioral changes following antisense oligonucleotide-induced reduction of organic cation transporter-3 in mice

The organic cation transporter-3 (OCT3) can transport monoamines, similar to neuronal monoamine transporters. Due to the lack of selective ligands, however, the functional role of OCT3 is still unknown. Thus, we investigated behavioral effects of antisense against OCT3 (AS) in mice. AS (0.075-0.25 microg/0.25 microl/h, for 7 days) dose-dependently decreased immobility time. Moreover, although neither AS (0.075 microg/0.25 microl/h, for 7 days) or imipramine (4 mg/kg, i.p.) were effective, imipramine (4 mg/kg, i.p.) significantly decreased immobility time in mice treated with AS (0.075 microg/0.25 microl/h, for 7 days). Additionally, AS (0.25 microg/0.25 microl/h, for 7 days) significantly increased locomotor activity induced by methamphetamine (1 mg/kg, s.c.), but did not affect spontaneous locomotor activity. These results suggest that OCT3 might become a novel molecular target to treat depression and other diseases related to monoaminergic neuronal systems.     

Inhibitory effects of Group I metabotropic glutamate receptors antagonists on the expression of NMDA receptor NR1 subunit in morphine tolerant rats

N-Methyl-d-aspartate receptor (NMDAR) and Group I metabotropic glutamate receptors (mGluRs) are involved in the process of morphine tolerance. Previous studies have shown that Group I mGluRs can modulate NMDAR functions in the central nervous system. The aim of the present study was to examine the influence of Group I mGluRs antagonists on the expression of NMDA receptor NR1 subunit (NR1) in the rat spinal cord. Morphine tolerance was induced in rats by repeated administration of 10 μg morphine (intrathecal, i.t.) twice a day for 7 consecutive days. Tail flick test was used to assess the effect of Group I mGluRs antagonist, AIDA ((RS)-1-Aminoindan-1,5 dicarboxylic acid) or mGluR5 antagonist, MPEP (2-methyl-6-(phenylethynyl)pyridine) on morphine antinociceptive tolerance. The expression of NR1 was measured by immunofluorescence and Western blot. Behavioral tests revealed that both AIDA and MPEP attenuated the development of morphine tolerance. The expression of NR1 was upregulated in the dorsal horn of spinal cord after chronic morphine treatment. AIDA or MPEP co-administered with morphine attenuated morphine induced upregulation of NR1. These findings suggest that the development of morphine tolerance partly prevented by Group I mGluRs antagonists may due to its inhibitory effect on the expression of NR1 subunit.     

大鼠纹状体I组代谢型谷氨酸受体激动引起动物向对侧旋转

目的:研究代谢型谷氨酸受体(mGluRs)激动剂引起大鼠向对侧旋转时介导的受体亚型。方法:大鼠纹状体内微量注射mGluRs激动剂或拮抗剂,观察大鼠的意识、行为变化,并于给药后6h测定旋转活动。结果:mGluRs非亚型特异的激动剂tACPD(500、1000nmol)纹状体内注射引起大鼠向对侧旋转,mGluRs的非竞争性拮抗剂L-AP₃、竞争性拮抗剂MCPG及抑制细胞内钙释放的胆罗啉均可减轻tACPD引起的旋转。I组mGluRs的特异性激动剂DHPG(500nmol)纹状体内注射也引起大鼠向对侧旋转,MCPG及mGluR₁的拮抗剂LY367385及mGluR₅的拮抗剂MPEP均可拮抗DHPG引起的旋转。预先腹腔注射利血平(5mg/kg)可阻断DHPG的作用。结论:I组mGluRs激动引起大鼠向对侧旋转,此作用可能与细胞内钙释放有关及依赖于多巴胺的存在。     

Effects of selective NMDA and non-NMDA blockade in the nucleus accumbens on the plus-maze test

Effect of blocking N-methyl-D-aspartic acid (NMDA) and non-NMDA-glutamatergic receptors on performance in the plus-maze was studied in male rats bilaterally cannulated into the nucleus accumbens (Acc). Rats were divided into seven groups that received either 1 microl injections of saline, (+/-)2-amino-7-phosphonoheptanoic acid (AP-7, 0.2, 0.5, or 1 microg) or 2,3 dioxo-6-nitro-1,2,3,4,tetrahydrobenzo-(f)quinoxaline-7-sulphonamide disodium (NBQX, 0.2, 0.5, or 1 microg) 15 min before testing. Time spent in open arm, time per entry, end arrivals, open, closed, and total arm entries, relationship between open-, closed-, and total arm entries, rearing, face-, head-, and body grooming, and number of fecal boli were recorded. Time spent in the open arm increased under AP-7 (0.5 and 1 microg; P<.01) and NBQX (1 microg; P<.05) treatment, whereas time per entry was increased only with AP-7 (1 microg; P<.05). Open arm entries were increased by the intermediate doses of AP-7 (0.5 microg; P<.01) and NBQX (0.5 microg; P<.05); end arrivals were increased by the intermediate dose of AP-7 (0.5 microg/1 microl, P<.05). The frequency of rearing, grooming, and closed arm entries was not affected by the treatment. We conclude that NMDA and non-NMDA-glutamatergic blockade in the Acc lead to a behavioral disinhibition of cortical influences with the median doses, but that at higher doses the blockers have an anxiolytic-like effect.     

Increase of spiny I activity in striatum after development of context-dependent sensitization of catalepsy in rats

In this study, it was investigated whether context-dependent sensitization of catalepsy changes the firing pattern in striatum. Rats were treated with either haloperidol (0.5 mg/kg i.p.) or saline, and tested on catalepsy with a concomitant single-unit measurement of the spiny I activity. Administration of haloperidol caused sensitization of catalepsy as measured on bar and grid. Concurrent within this behavioral change, spike-frequency increased over the course of the testing days in haloperidol-treated rats whereas the spike-frequency remained unchanged in saline-treated animals. Burst-frequency remained unchanged within both treatment groups over the days. In conclusion, sensitization of catalepsy is represented by striatal cellular activity as indicated by increases in spike-frequency of spiny I neurons.     

Dopaminergic regulation of striatal proenkephalin mRNA and prodynorphin mRNA: contrasting effects of D1 and D2 antagonists

In situ hybridization was used to measure the levels of proenkephalin mRNA and prodynorphin mRNA in regions of rat striatum and nucleus accumbens. Chronic administration of haloperidol (2.4 mg/kg/day for 7 days) increased the levels of proenkephalin mRNA in both striatum and nucleus accumbens. In contrast, the levels of prodynorphin mRNA were not significantly affected in any region. Chronic administration of the D1 antagonist SCH 23390 (2.4 mg/kg/day for 7 days) decreased the striatal content of proenkephalin mRNA. A similar effect was seen in the lateral nucleus accumbens. The levels of prodynorphin mRNA were unaffected by SCH 23390 treatment in all regions examined. These results suggest that there is no major tonic dopaminergic regulation of prodynorphin synthesis in the basal ganglia. However, it appears that there is a tonic suppression, via D2 receptors, and a tonic enhancement, via D1 receptors, of proenkephalin synthesis, in the striatum and nucleus accumbens.     

Combined intrastriatal dopamine D1 and serotonin 5-HT2 receptor stimulation reveals a mechanism for hyperlocomotion in 6-hydroxydopamine-lesioned rats

Loss of dopaminergic innervation to the striatum increases the sensitivity of dopamine (DA) D1 and serotonin (5-HT) 5-HT2 receptor signaling. Previous work from our laboratory has shown that systemic co-administration of D1 and 5-HT2 receptor agonists leads to the synergistic overexpression of striatal preprotachykinin mRNA levels in the DA-depleted, but not intact animals. In the present study, we examined this mechanism as related to locomotor behavior. Adult male Sprague-Dawley rats were subject to bilateral i.c.v. 6-hydroxydopamine (6-OHDA; 200 microg in 10 microl/side) or vehicle (0.9% saline and 0.1% ascorbic acid). After 3 weeks, rats were tested for locomotor responses to bilateral intrastriatal infusions of vehicle (0.9% NaCl), the D1 agonist SKF82958 [(+/-)6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetra-hydro-(1H)-3-benzazepine hydrobromide; 0.1, 1.0 or 10.0 microg/side], the 5-HT2 agonist DOI [(+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane; 0.1, 1.0 or 10.0 microg/side] or subthreshold doses of DOI and SKF82958 (0.1 microg+0.1 microg in 0.8 microl/side). Rats with DA loss demonstrated supersensitive locomotor responses to SKF82958, but not DOI. Combined administration of subthreshold SKF82958 and DOI doses (0.1 microg+0.1 microg) synergistically increased locomotor behavior only in 6-OHDA-lesioned rats. These effects were blocked by either the D1 antagonist SCH23390 3-methyl-1-phenyl-2,3,4,5-tetrahydro-7-chloro-8-hydroxy-(1H)-3-benzazepine or the 5-HT2 antagonist ritanserin (each 1.0 microg in 0.8 microl/side).The results of this study suggest that the behavioral synergy induced by local co-stimulation of D1 and 5-HT2 receptors within the 6-OHDA-lesioned striatum may lead to hyperkinesias that can occur with continued pharmacological treatment of Parkinson's disease.     

Repeated cocaine administration increases B-cell leukemia/lymphoma 2 phosphorylation in the rat dorsal striatum

Protein phosphorylation caused by drug administration is a critical step in the regulation of behavioral alterations. This study was conducted to determine how repeated exposure to cocaine phosphorylates B-cell leukemia/lymphoma 2 (Bcl2), which may be responsible for the regulation of behavioral alterations in the rat dorsal striatum. The results revealed that repeated systemic injections of cocaine (20 mg/kg) once a day for 7 consecutive days increased the phosphorylation of Bcl2 at serine 70 (Bcl2-S70). However, this increase was reduced by the blockade of dopamine D1 receptors, group I metabotropic glutamate receptors (mGluRs), and N-methyl-d-aspartate (NMDA) receptors. In addition, elevation of behavioral locomotor activity after repeated exposure to cocaine was partially reduced by the inhibition of Bcl2. These data suggest that stimulation of dopamine D1 receptors, group I mGluRs, and NMDA receptors following repeated cocaine administration is necessary for the induction of Bcl2-S70 phosphorylation, which contributes to the expression of behavioral sensitization.     

Involvement of NO in the convulsive behavior and oxidative damage induced by the intrastriatal injection of methylmalonate

Acute intrastriatal administration of methylmalonic acid (MMA) induces convulsions through NMDA receptor-mediated mechanisms and increases production of end products of oxidative damage. Although it has been demonstrated that nitric oxide (NO) production increases with NMDA receptor stimulation and contributes to the oxidative damage observed in several neurodegenerative disorders, the role of NO in MMA-induced convulsions has not been investigated to date. In the present study we investigated the effects of the intrastriatal injection of N(omega)-nitro-L-arginine methyl ester (L-NAME: 10(-4) to 10(0) nmol/0.5 microl) on the convulsions and striatal protein carbonylation induced by the intrastriatal injection of MMA (4.5 micromol/1.5 microl). l-NAME (10(-3) to 10(-1)nmol) protected against MMA-induced convulsions and protein carbonylation ex vivo. These results suggest the involvement of NO in the convulsive behavior and protein carbonylation elicited by MMA.