Entopeduncular Nucleus Projections to the Lateral Habenula Contribute to Cocaine Avoidance.

The aversive properties associated with drugs of abuse influence both the development of addiction and relapse. Cocaine produces strong aversive effects after rewarding effects wear off, accompanied by increased firing in the lateral habenula (LHb) that contributes to downstream activation of the rostromedial tegmental nucleus (RMTg). However, the sources of this LHb activation are unknown, as the LHb receives many excitatory inputs whose contributions to cocaine aversion remain uncharacterized. Using cFos activation and in vivo electrophysiology in male rats, we demonstrated that the rostral entopeduncular nucleus (rEPN) was the most responsive region to cocaine among LHb afferents examined and that single cocaine infusions induced biphasic responses in rEPN neurons, with inhibition during cocaine's initial rewarding phase transitioning to excitation during cocaine's delayed aversive phase. Furthermore, rEPN lesions reduced cocaine-induced cFos activation by 2-fold in the LHb and by a smaller proportion in the RMTg, while inactivation of the rEPN or the rEPN-LHb pathway attenuated cocaine avoidance behaviors measured by an operant runway task and by conditioned place aversion (CPA). These data show an essential but not exclusive role of rEPN and its projections to the LHb in processing the aversive effects of cocaine, which could serve as a novel target for addiction vulnerability.SIGNIFICANCE STATEMENT Cocaine produces well-known rewarding effects but also strong aversive effects that influence addiction propensity, but whose mechanisms are poorly understood. We had previously reported that the lateral habenula (LHb) is activated by cocaine and contributes to cocaine's aversive effects, and the current findings show that the rostral entopeduncular nucleus (rEPN) is a major contributor to this LHb activation and to conditioned avoidance of cocaine. These findings show a critical, though not exclusive, rEPN role in cocaine's aversive effects, and shed light on the development of addiction.

Globus pallidus, but not entopeduncular nucleus, 6-OHDA-induced lesion attenuates L-Dopa-induced dyskinesia in the rat model of Parkinson's disease.

Although extrastriatal dopaminergic (DAergic) systems are being recognized as contributors to Parkinson's disease (PD) pathophysiology, the role of extrastriatal DA depletion in L-Dopa-induced dyskinesia (LID) is still unknown. In view of the physiologic actions of DA on pallidal neuronal activity and the effects on motor behavior of local injection of DA drugs, the loss of the external (GPe, GP in rodents) and internal (GPi, entopeduncular nucleus (EP) in rodents) pallidal DAergic innervation might differentially contribute to LID. A role of pallidal serotonergic (SER) terminals in LID has been highlighted, however, the effect of DAergic innervation is unknown. We investigated the role of DAergic pallidal depletion on LID. Rats were distributed in groups which were concomitantly lesioned with 6-OHDA or vehicle (sham) in the GP, or EP, and in the medial forebrain bundle (MFB) as follows: a) MFB-sham+GP-sham, b) MFB-sham+GP-lesion, c) MFB-lesion+GP-sham, d) MFB-lesion+GP-lesion, e) MFB-sham+EP-sham, f) MFB-sham+EP-lesion, g) MFB-lesion+EP-sham, and h) MFB-lesion+EP-lesion. Four weeks later, animals were treated with L-Dopa (6 mg/kg) twice daily for 22 days.. Immunohistochemical studies were performed in order to investigate the changes in pallidal SER and serotonin transporter (SERT) levels. GP, but not EP, DAergic denervation attenuated LID in rats with a concomitant MFB lesion (p < 0.01). No differences were found in GP SERT expression between groups of animals developing or not LID. These results provide evidence of the relevance of GP DAergic innervation in LID. The conversion of levodopa to DA in GP serotonergic nerve fibers appears not to be the major mechanism underlying LID.

Inactivation of endopeduncular nucleus impaired fear conditioning and hippocampal synaptic plasticity in rats.

The internal globus pallidus (GPi) is one part of basal ganglion nucleuses which play fundamental role in motor function. Recent studies indicated that GPi could modulate emotional processing and learning, but the possible mechanism remains still unknown. In this study, the effects of endopeduncular nucleus (EP, a rodent homolog of GPi) on fear conditioning were tested in rats. GABAA receptor agonist muscimol was bilaterally delivered into the EP 15 min before or immediately after fear conditioning in rats. We found that EP inactivation impaired the acquisition but not consolidation of fear memory in rats. Furthermore, the long-term potentiation (LTP) in hippocampal CA1 area was impaired, and the learning related phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) subunit 1 (GluA1) at the Ser845 site in hippocampus was decreased in muscimol treated group. These results demonstrated that dysfunction of EP impaired hippocampal dependent learning and memory in rats.

Botulinum toxin A injection into the entopeduncular nucleus improves dynamic locomotory parameters in hemiparkinsonian rats.

Parkinson's disease is associated with hyperactivity of the subthalamic nucleus (STN), contributing to motor and gait disturbances. Although deep brain stimulation of the STN alleviates certain motor dysfunction, its specific effect on gait abnormalities remains controversial. This study investigated the long-term changes in locomotion following direct infusions of botulinum toxin-A into the globus pallidus internal segment (GPi) to suppress the flow of information from the STN to the GPi in a hemiparkinsonian rat model. Static and dynamic gait parameters were quantified using a CatWalk apparatus. Interestingly, botulinum toxin-A at 0.5 ng significantly reduced only the dynamic gait parameters of hemiparkinsonian rats at 1 week and 1 month post-infusion, while static gait parameters did not change. This study offers new insights into the complexity of basal ganglia in locomotor control and shows the potential of central infusion of botulinum toxin-A as a novel intervention in the study of experimental hemiparkinson's disease.

Acute L-DOPA administration reverses changes in firing pattern and low frequency oscillatory activity in the entopeduncular nucleus from long term L-DOPA treated 6-OHDA-lesioned rats.

The pathophysiology of Parkinson's disease (PD) and L-DOPA-induced dyskinesia (LID) is associated with aberrant neuronal activity and abnormal high levels of oscillatory activity and synchronization in several basal ganglia nuclei and the cortex. Previously, we have shown that the firing activity of neurons in the substantia nigra pars reticulata (SNr) is relevant in dyskinesia and may be driven by subthalamic nucleus (STN) hyperactivity. Conversely, low frequency oscillatory activity and synchronization in these structures seem to be more important in PD because they are not influenced by prolonged L-DOPA administration. The aim of the present study was to assess (through single-unit extracellular recording techniques under urethane anaesthesia) the neuronal activity of the entopeduncular nucleus (EPN) and its relationship with LID and STN hyperactivity, together with the oscillatory activity and synchronization between these nuclei and the cerebral cortex in 6-OHDA-lesioned rats that received long term L-DOPA treatment (or not). Twenty-four hours after the last L-DOPA injection the firing activity of EPN neurons in long term L-DOPA treated 6-OHDA-lesioned rats was more irregular and bursting compared to sham rats, being those alterations partially reversed by the acute challenge of L-DOPA. No correlation between EPN neurons firing activity and abnormal involuntary movements score was found. However, there was a significant correlation between the firing activity parameters of EPN and STN neurons recorded from long term L-DOPA treated 6-OHDA-lesioned rats. Low frequency oscillatory activity and synchronization both within the EPN and with the cerebral cortex were enhanced in 6-OHDA-lesioned animals. These changes were reversed by the acute L-DOPA challenge only in long term L-DOPA treated 6-OHDA-lesioned rats. Altogether, these results obtained from long term L-DOPA treated 6-OHDA-lesioned rats suggest (1) a likely relationship between STN and EPN firing patterns and spiking phases induced by changes after prolonged L-DOPA administration and (2) that the effect of L-DOPA on the firing pattern, low frequency oscillatory activity and synchronization in the EPN may have a relevant role in LID.

Cocaine withdrawal reduces GABAB R transmission at entopeduncular nucleus - lateral habenula synapses.

Lateral habenula (LHb) hyperactivity plays a pivotal role in the emergence of negative emotional states, including those occurring during withdrawal from addictive drugs. We have previously implicated cocaine-driven adaptations at synapses from the entopeduncular nucleus (EPN) to the LHb in this process. Specifically, ionotropic GABAA receptor (R)-mediated neurotransmission at EPN-to-LHb synapses is reduced during cocaine withdrawal, due to impaired vesicle filling. Recent studies have shown that metabotropic GABAB R signaling also controls LHb activity, although its role at EPN-to-LHb synapses during drug withdrawal is unknown. Here, we predicted that cocaine treatment would reduce GABAB R-mediated neurotransmission at EPN-to-LHb synapses. We chronically treated mice with saline or cocaine, prepared brain slices after two days of withdrawal and performed voltage-clamp recordings from LHb neurons whilst optogenetically stimulating EPN terminals. Compared with controls, mice in cocaine withdrawal exhibited reduced GABAA R-mediated input to LHb neurons, and a reduced occurrence of GABAB R-signaling at EPN-to-LHb synapses. We then assessed the underlying mechanism of this decrease. Application of GABAB R agonist baclofen evoked similar postsynaptic responses in EPN-innervated LHb neurons in saline- and cocaine-treated mice. Release probability at EPN-to-LHb GABAergic synapses was also comparable between groups. However, incubating brain slices in glutamine to facilitate GABA vesicle filling, normalized GABAB R-currents at EPN-to-LHb synapses in cocaine-treated mice. Overall, we show that during cocaine withdrawal, together with reduced GABAA R transmission, also GABAB R-mediated inhibitory signaling is diminished at EPN-to-LHb synapses, likely via the same presynaptic deficit. In concert, these alterations are predicted to contribute to the emergence of drug withdrawal symptoms, facilitating drug relapse.

Intrapallidal injection of botulinum toxin A recovers gait deficits in a parkinsonian rodent model.

AIM: Modulation of electrical activity in the subthalamic nucleus has been therapeutically effective in Parkinson's disease. Pharmacological manipulation of glutamate release from subthalamic neurons could also favourably alter basal ganglia activity to improve motor symptoms. This study investigates the efficacy of selective suppression of hyperactive glutamatergic input from the subthalamic nucleus to the globus pallidus internal segment by botulinum toxin A (BoNT-A) in a parkinsonian model. METHODS: Unilateral 6-hydroxydopamine lesioned parkinsonian rodents and controls received microinfusions of BoNT-A or vehicle into the ipsilateral internal globus pallidus (n = 8 per group). Changes in gait were measured by the CatWalk apparatus, along with assessment of apomorphine-induced rotational behaviour prior to and following BoNT-A injection. Immunofluorescent staining for markers of glutamatergic, GABAergic and total terminals was performed at the internal globus pallidus. RESULTS: Administration of a single dose of BoNT-A (0.5 ng) significantly improved the rotational asymmetry and gait abnormalities. Ameliorations in speed, body speed variation, cadence and walking pattern were comparable to pre-lesioned animals, and persisted up to 1 month following BoNT-A injection. These changes are associated to BoNT-A's ability to selectively target glutamatergic terminals. CONCLUSION: Blockade of subthalamic hyperactivity by BoNT-A leads to sufficient reorganization in the basal ganglia needed to generate a consistent rhythmic pattern of walking. This suggests the potential use of intracerebral BoNT-A to produce effective neuromodulation in the parkinsonian brain, as well as expansion into other neurodegenerative disorders linked to excitotoxity.

Coherence of neuronal firing of the entopeduncular nucleus with motor cortex oscillatory activity in the 6-OHDA rat model of Parkinson's disease with levodopa-induced dyskinesias.

The pathophysiological mechanisms leading to dyskinesias in Parkinson's disease (PD) after long-term treatment with levodopa remain unclear. This study investigates the neuronal firing characteristics of the entopeduncular nucleus (EPN), the rat equivalent of the human globus pallidus internus and output nucleus of the basal ganglia, and its coherence with the motor cortex (MCx) field potentials in the unilateral 6-OHDA rat model of PD with and without levodopa-induced dyskinesias (LID). 6-hydroxydopamine-lesioned hemiparkinsonian (HP) rats, 6-OHDA-lesioned HP rats with LID (HP-LID) rats, and naïve controls were used for recording of single-unit activity under urethane (1.4 g/kg, i.p) anesthesia in the EPN "on" and "off" levodopa. Over the MCx, the electrocorticogram output was recorded. Analysis of single-unit activity in the EPN showed enhanced firing rates, burst activity, and irregularity compared to naïve controls, which did not differ between drug-naïve HP and HP-LID rats. Analysis of EPN spike coherence and phase-locked ratio with MCx field potentials showed a shift of low (12-19 Hz) and high (19-30 Hz) beta oscillatory activity between HP and HP-LID groups. EPN theta phase-locked ratio was only enhanced in HP-LID compared to HP rats. Overall, levodopa injection had no stronger effect in HP-LID rats than in HP rats. Altered coherence and changes in the phase lock ratio of spike and local field potentials in the beta range may play a role for the development of LID.

Dopamine D1 Receptor-Mediated Transmission Maintains Information Flow Through the Cortico-Striato-Entopeduncular Direct Pathway to Release Movements.

In the basal ganglia (BG), dopamine plays a pivotal role in motor control, and dopamine deficiency results in severe motor dysfunctions as seen in Parkinson's disease. According to the well-accepted model of the BG, dopamine activates striatal direct pathway neurons that directly project to the output nuclei of the BG through D1 receptors (D1Rs), whereas dopamine inhibits striatal indirect pathway neurons that project to the external pallidum (GPe) through D2 receptors. To clarify the exact role of dopaminergic transmission via D1Rs in vivo, we developed novel D1R knockdown mice in which D1Rs can be conditionally and reversibly regulated. Suppression of D1R expression by doxycycline treatment decreased spontaneous motor activity and impaired motor ability in the mice. Neuronal activity in the entopeduncular nucleus (EPN), one of the output nuclei of the rodent BG, was recorded in awake conditions to examine the mechanism of motor deficits. Cortically evoked inhibition in the EPN mediated by the cortico-striato-EPN direct pathway was mostly lost during suppression of D1R expression, whereas spontaneous firing rates and patterns remained unchanged. On the other hand, GPe activity changed little. These results suggest that D1R-mediated dopaminergic transmission maintains the information flow through the direct pathway to appropriately release motor actions.

High-Frequency Stimulation of the Rat Entopeduncular Nucleus Does Not Provide Functional or Morphological Neuroprotection from 6-Hydroxydopamine.

Deep brain stimulation (DBS) is the most common neurosurgical treatment for Parkinson's disease (PD). Whereas the globus pallidus interna (GPi) has been less commonly targeted than the subthalamic nucleus (STN), a recent clinical trial suggests that GPi DBS may provide better outcomes for patients with psychiatric comorbidities. Several laboratories have demonstrated that DBS of the STN provides neuroprotection of substantia nigra pars compacta (SNpc) dopamine neurons in preclinical neurotoxin models of PD and increases brain-derived neurotrophic factor (BDNF). However, whether DBS of the entopeduncular nucleus (EP), the homologous structure to the GPi in the rat, has similar neuroprotective potential in preclinical models has not been investigated. We investigated the impact of EP DBS on forelimb use asymmetry and SNpc degeneration induced by 6-hydroxydopamine (6-OHDA) and on BDNF levels. EP DBS in male rats received unilateral, intrastriatal 6-OHDA and ACTIVE or INACTIVE stimulation continuously for two weeks. Outcome measures included quantification of contralateral forelimb use, stereological assessment of SNpc neurons and BDNF levels. EP DBS 1) did not ameliorate forelimb impairments induced by 6-OHDA, 2) did not provide neuroprotection for SNpc neurons and 3) did not significantly increase BDNF levels in any of the structures examined. These results are in sharp contrast to the functional improvement, neuroprotection and BDNF-enhancing effects of STN DBS under identical experimental parameters in the rat. The lack of functional response to EP DBS suggests that stimulation of the rat EP may not represent an accurate model of clinical GPi stimulation.

Mood regulation. GABA/glutamate co-release controls habenula output and is modified by antidepressant treatment.

The lateral habenula (LHb), a key regulator of monoaminergic brain regions, is activated by negatively valenced events. Its hyperactivity is associated with depression. Although enhanced excitatory input to the LHb has been linked to depression, little is known about inhibitory transmission. We discovered that γ-aminobutyric acid (GABA) is co-released with its functional opponent, glutamate, from long-range basal ganglia inputs (which signal negative events) to limit LHb activity in rodents. At this synapse, the balance of GABA/glutamate signaling is shifted toward reduced GABA in a model of depression and increased GABA by antidepressant treatment. GABA and glutamate co-release therefore controls LHb activity, and regulation of this form of transmission may be important for determining the effect of negative life events on mood and behavior.

High-frequency electrical stimulation of the subthalamic nucleus excites target structures in a model using c-fos immunohistochemistry.

Deep-brain stimulation at high frequencies (HFS) directed to the subthalamic nucleus (STN) is used increasingly to treat patients with Parkinson's disease. However, the mechanism of action by which HFS of the STN achieves its therapeutic effects remains unresolved. Insofar as lesions of the STN have similar therapeutic benefit, a favored hypothesis is that HFS acts by suppressing neural activity in the STN. The purpose of the present study was to exploit prior observations that exposure to ether anesthesia in a rodent model evokes c-fos expression (a marker of neural activation) in the STN and its efferent structures, the globus pallidus, entopeduncular nucleus and substantia nigra. We showed first that exposure to ether induced a profound oscillatory pattern of neural activity in the STN and SNr, which could explain the marked induction of c-fos immunoreactivity in these structures. Secondly, inhibition of the STN by local injections of the GABA agonist, muscimol, suppressed ether-evoked c-fos expression in all target structures. This showed that excitation of target structures in the ether model originated, at least in part, from the STN. Thirdly, and contrary to expectation, HFS of the STN increased further the expression of c-fos in the STN target structures of animals treated with ether. Finally, we demonstrated, in the absence of ether treatment, that HFS and chemical stimulation of the STN with local injections of kainic acid both induced c-fos expression in the globus pallidus, entopeduncular nucleus and substantia nigra. Together these results suggest that the principal action of STN stimulation at high frequencies is to excite rather than inhibit its efferent targets. Given that Parkinsonism has been associated with increased levels of inhibitory output activity from the basal ganglia, it is unlikely that excitation of output structures revealed in this study provides a basis for deep-brain stimulation's therapeutic action.

Entopeduncular nucleus endocannabinoid system modulates sleep-waking cycle and mood in rats.

Since the pioneering work of Gadea-Ciria (Gadea-Ciria M, Stadler H, Lloyd KG, Bartholini G. Acetylcholine release within the cat striatum during the sleep-wakefulness cycle. Nature 1973; 243:518-519) indicating pointing to the involvement of acetylcholine and basal ganglia in sleep regulation; extensive literature has suggested that this brain complex participates in the control of the sleep-waking cycle (SWC). On the other hand, it has been demonstrated that the endocannabinoid system (eCBS) is prominently involved in the regulation of the SWC, mood and its related disorders. Since cannabinoid receptor 1 (CB1R) is highly expressed in basal ganglia, in particular in the entopeduncular nucleus (EP), we believe that it is important to know what the role of the EP CB1R is on SWC, depression, and anxiety. To provide insight into the role of the EP CB1R in the regulation of wakefulness (W), non-rapid eye movement sleep (NREMs) and rapid eye movement sleep (REMs), rats were recorded for 24h immediately after a single intra-EP administration of N-arachidonoylethanolamine (AEA) or 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-(1-piperidyl)pyrazole-3-carboxamide (AM251; CB1 inverse agonist). Likewise, the effect of these drugs on anxiety and depression was tested by means of the elevated plus maze (EPM) and forced swim test (FST), respectively. Results demonstrate that AEA increases NREMs expression, while AM251 increases W and decreases both NREMs and REMs. In addition, administration of AM251 decreases the time rats spent in the open arms and increases immobility time in the FST. It seems that activation of the CB1R in the EP is important to induce sleep, while its blockade promotes W, as well as anxiety and depression, somewhat resembling insomnia in humans. These results suggest that the EP CB1R is modulating sleep and mood.

The enhanced oral response to the 5-HT2 agonist Ro 60-0175 in parkinsonian rats involves the entopeduncular nucleus: electrophysiological correlates.

Lesions of nigrostriatal dopaminergic neurons as seen in Parkinson's disease (PD) increase orofacial responses to serotonergic (5-HT) agonists in rodents. Although this response to 5-HT agonists has been related to aberrant signalling in the basal ganglia, a group a subcortical structures involved in the control of motor behaviours, it deserves additional studies with respect to the specific loci involved. Using measurements of orofacial activity, as well as single-cell recordings in vivo, we have studied the role of the entopeduncular nucleus (EPN; equivalent to the internal globus pallidus of primates), an output structure of basal ganglia, in the hypersensitized responses to a 5-HT agonist in sham- or unilaterally dopamine-depleted rats. Intra-EPN injections of Ro 60-0175 (0.3 and 1 µg/100 nl) promoted robust oral movements in 6-OHDA rats without affecting oral activity in sham-depleted rats. Peripheral administration of Ro 60-0175 (3 mg/kg ip) decreased EPN neuronal firing rate in 6-OHDA rats compared to sham-depleted rats. Such an effect was also observed when the agonist (0.2 µg/20 nl) was locally applied onto EPN neurons. These data demonstrate the contribution of EPN to hypersensitized responses to 5-HT agonists in a rat model of PD.

l-dopa-induced dyskinesias in unilateral 6-hydroxydopamine-lesioned rats are not modified by excitotoxic lesion of the entopeduncular nucleus and substantia nigra pars reticulata.

l-Dopa-induced dyskinesias (LIDs) are a troublesome complication in Parkinson's disease after long-term therapy and a major reason for surgical treatment. LIDs are effectively eliminated by surgery. We aimed to reproduce such effect in the 6-hydroxydopamine (6-OHDA)-lesioned rat model. Single or combined lesions with quinolinic acid were caused in the entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNr) on 6-hydroxydopamine (6-OHDA)-lesioned rats treated for 3 weeks with l-Dopa (6 mg/kg plus 15 mg/kg benserazide, i.p.). l-Dopa administration was continued for a further week following the lesion and abnormal involuntary movements (AIMs) scored at the end of treatment. Neither the individual lesions of the EP and SNr nor the combined lesions had any antidyskinetic effect nor decreased the total number of rotations. These results suggest that excitotoxic lesions of neurons bodies of the output nuclei of the basal ganglia, which destroy cell bodies and spare fibers of passage, do not induce a beneficial reduction of dyskinesias in contrast to thermolytic lesions in humans (which provokes a complete tissue destruction), thus supporting the possibility that other nuclei or systems might be involved in the antidyskinetic effect of pallidotomy.

Endocannabinoid/GABA interactions in the entopeduncular nucleus modulates alcohol intake in rats.

Alcohol use disorder is a compulsive behavior driven by motivational systems and by a poor control of consummatory behavior. The entopeduncular nucleus (EP) seems to be involved in the regulation of executive mechanisms, hence, in the expression of behavior. Endocannabinoids (eCB) are involved in alcohol intake mechanisms. The eCB receptor name cannabinoid receptor 1 (CB1R) is expressed in the EP in GABAergic terminals. The role of the eCB system (eCBs) of the EP in the modulation of alcohol seeking and intake behavior is unknown. Therefore, we decided to investigate the role of the eCBs and its interaction with GABA transmission in rat EP, in the regulation of alcohol intake behavior. Rats were submitted to a 10-day period of moderate alcohol (10% in tap water) ingestion. No tap water was available. On day 11, either anandamide (AEA, CB1 receptor agonist), AM251 (CB1R inverse agonist), baclofen (BAC, GABAB receptor agonist), or CGP35348 (GABAB receptor antagonist) was administered into the EP. One bottle of water and one of alcohol (10% in water) were available ad libitum for the following 24 h, and consumption was quantified at the end of this period. Results show that administration of AEA into the EP decreased alcohol consumption while AM251 and BAC administered independently increased alcohol consumption. AEA prevented the increase induced by AM251 or BAC. Likewise, CGP35348 prevented alcohol ingestion induced by AM251. These data suggest that eCBs dysfunction in the EP may be playing a crucial role in the abuse and dependence of alcohol and other drugs.

Activity modulation of the globus pallidus and the nucleus entopeduncularis affects compulsive checking in rats.

Deep brain stimulation at high frequencies (HFS) is currently studied in the treatment of therapy-refractory obsessive-compulsive disorder (OCD). The diversity of targeted brain areas and the discrepancy in demonstrating beneficial effects, highlight the need for better mapping of brain regions in which HFS may yield anti-compulsive effects. This goal may be achieved by investigating the effects of HFS in appropriate animal models of OCD. The present study tested the effect of bilateral HFS or pharmacological inactivation (as induced by intracerebral administration of the GABA-agonist muscimol) of both the Globus pallidus (GP; rodent equivalent to human GP externus) and the Nucleus entopeduncularis (EP; rodent equivalent to human GP internus) on checking behaviour in the quinpirole rat model of OCD. We demonstrate that HFS of the GP does not and HFS of the EP only partially reduces OCD-like behaviour in rats. In contrast, pharmacological inactivation of both GP and EP significantly reduces OCD-like behaviour in the model. These data contrast previously derived data on the effectiveness of HFS of the subthalamic nucleus, nucleus accumbens, GP and EP in the same and other rat models of OCD. We conclude that (i) although GP and EP play an important role in the pathophysiology of OCD, these areas may not represent first choice target structures for HFS, (ii) the effectiveness of HFS may depend on different subtypes of OCD, represented in different animal models, and (iii) differential net mechanisms may subserve the effectiveness of HFS and pharmacological inactivation.

Effects of pharmacological entopeduncular manipulations on idiopathic dystonia in the dt(sz) mutant hamster.

The pathophysiology of idiopathic dystonias is still unknown, but it is regarded as a basal ganglia disorder. Previous experiments in the dt(sz) hamster, a model of primary paroxysmal dystonia, demonstrated reduced discharge rates and an abnormal pattern within the entopeduncular nucleus (EPN), a basal ganglia output structure. To clarify if this is based on abnormal gamma-aminobutyric acid(GABA)ergic or glutamatergic input, microinjections into the EPN were done in mutant hamsters in the present study. The GABA(A) receptor antagonists pentylenetetrazole and bicuculline exerted moderate antidystonic effects, while previous systemic administrations worsened dystonia in the dt(sz) mutant. GABA-potentiating drugs, i.e., the GABA(A) receptor agonist muscimol and the GABA transporter inhibitor 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxy-lic acid (NNC-711), which are known to improve dystonia after systemic treatment in mutant hamsters, did not exert significant effects after EPN injections, but NNC-711 tended to increase the severity at the highest dose (2.5 ng bilateral). The NMDA receptor antagonist D(-)-2-amino-5-phosphopentanoic acid (AP-5) retarded the onset of a dystonic attack. However, this effect was not dose dependent and the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol(f)quinoxaline (NBQX) alone or in combination with AP-5 and NNC-711, also failed to show any effects on dystonia. The present data do not provide clear evidence for an enhanced striatal GABAergic input or a reduced glutamatergic activation of the EPN via the subthalamic nucleus, i.e., more pronounced antidystonic effects of GABA(A) receptor antagonists and stronger prodystonic effects of GABAmimetics and glutamate receptor antagonists were expected. Nevertheless, previously found changes in entopeduncular activity probably play a critical pathophysiological role in dystonic hamsters.

Influences of entopeduncular nucleus stimulation upon electromyogram activity of masticatory muscles.

Influences of stimulation of the entopeduncular nucleus (Ep) upon electromyogram (EMG) activity of masticatory muscles were examined. In the rat lightly anesthetized with halothane, high frequency (HF) microstimulation (trains of 20, 333-Hz cathodal pulses at 30-60 microA) and GABA microinjection (0.2-0.6 microl of 10 mM GABA dissolved in physiological saline) were performed in the Ep by using a three-barreled microelectrode. EMG activity was recorded from the anterior digastrics and the anterior superficial masseter muscles by using two fine enamel-insulated copper wires. The EMG activity was also evoked by the GABA microinjection. The effect of the GABA microinjection was negated by the microinjection of bicuculline prior to the GABA microinjection. The EMG activity was classified into the tonic spike-type, burst-type, or mixed type on the basis of the waveform. In each rat, the location of the microelectrode tip was estimated by observing a series of serial frontal sections through the whole rostrocaudal extent of the Ep. The present data suggested that Ep neurons involved in elicitation of tonic spike-type activity in the jaw muscles might be located mainly in the rostral third of the Ep, and that Ep neurons implicated in provocation of burst-type activity in jaw muscles might be located in the caudal third of the Ep. Possible neuronal pathways from the Ep to motoneurons innervating the masticatory muscles were discussed. The present data shed new light on the control mechanisms of the basal ganglia upon jaw movements.

Modulation of torsinA expression in the globus pallidus internus is associated with levodopa-induced dyskinesia in hemiparkinsonian rats.

TorsinA is the causative protein of DYT1 dystonia, a major representative of hyperkinetic movement disorders. In this study, the distribution of torsinA was investigated in the basal ganglia of hemiparkinsonian rats with or without levodopa-induced dyskinesia (LID). Two months after 6-hydroxydopamine (OHDA) treatment, Wistar-albino rats were subjected to intermittent intraperitoneal injection of levodopa/benserazid (LID-group, n=5) or vehicle (control, n=5) for 21 days. Immunohistochemical analysis disclosed that in the caudal portion of the entopeduncular nucleus (EP), homologous to the globus pallidus internus (GPi) in primates, on the parkinsonian side, there was a significant decrease of torsinA-immunopositive neurons in rats with LID, but not in those without LID. However, Nissl-staining showed no loss of GPi neurons in rats with LID. In both groups, there was no significant difference between ipsi- and contralateral sides with respect to the density of torsinA-positive neuronal cells in the striatum, globus pallidus externus, and subthalamic nucleus. Ours are the first data to demonstrate the specific modulation of torsinA expression in the basal ganglia of the hyperkinesia model, suggesting that GPi neurons containing torsinA possess pathologic plasticity for LID.