Modulatory effects of the GABAergic basal ganglia neurons on the PPN and the muscle tone inhibitory system in cats

Pedunculopontine tegmental nucleus (PPN) contributes to the control muscle tone by modulating the activities of pontomedullary reticulospinal systems during wakefulness and rapid eye movement (REM) sleep. The PPN receives GABAergic projection from the substantia nigra pars reticulata (SNr), an output nucleus of the basal ganglia. Here we examined how GABAergic SNr-PPN projection controls the activity of the pontomedullary reticulospinal tract that constitutes muscle tone inhibitory system. Intracellular recording was made from 121 motoneurons in the lumbosacral segments in decerebrate cats (n=14). Short train pulses of stimuli (3 pulses with 5 ms intervals, 10-40 mA) applied to the PPN, where cholinergic neurons were densely distributed, evoked eye movements toward to the contralateral direction and bilaterally suppressed extensor muscle activities. The identical PPN stimulation induced IPSPs, which had a peak latency of 40-50 ms with a duration of 40-50 ms, in extensor and flexor motoneurons. The late-latency IPSPs were mediated by chloride ions. Microinjection of atropine sulfate (20 mM, 0.25 ml) into the pontine reticular formation (PRF) reduced the amplitude of the IPSPs. Although conditioning stimuli applied to the SNr (40-60 mA and 100 Hz) alone did not induce any postsynaptic effects on motoneurons, it reduced the amplitude of the PPN-induced IPSPs. Subsequent injection of bicuculline (5 mM, 0.25 ml) into the PPN blocked the SNr effects. Microinjections of NMDA (5 mM, 0.25 ml) and muscimol (5 mM, 0.25 ml) into the SNr reduced and increased the amplitude of the PPN-induced IPSPs, respectively. These results suggest that GABAergic basal ganglia output controls postural muscle tone by modulating the activity of cholinergic PPN neurons which activate the muscle tone inhibitory system. The SNr-PPN projection may contribute to not only control of muscle tone during movements in wakefulness but also modulation of muscular atonia of REM sleep. Dysfunction of the SNr-PPN projection may therefore be involved in sleep disturbances in basal ganglia disorders.     

GABAA Receptors in the Pars Compacta and GABAB Receptors in the Pars Reticulata of Rat Substantia Nigra Modulate the Striatal Dopamine Release

The nigral GABAergic regulation of striatal dopamine release was investigated using voltammetry in freely moving rats. The local administration of muscimol (1 nM) in the substantia nigra pars compacta, but not in the substantia nigra pars reticulata, increased the striatal dopamine release. In contrast, the administration of baclofen (10 nM) in the substantia nigra pars reticulata, but not in the substantia nigra pars compacta, produced a decrease of the striatal dopamine release. Opposite effects were respectively observed after administration of GABA_A and GABA_B antagonists. These data lead us to suggest a differential presynaptic GABAergic control of the dopaminergic neurotransmission through GABA_A receptors in the substantia nigra pars compacta, and GABA_B receptors in the substantia nigra pars reticulata.     

Disinhibition of nigral GABA output neurons mediates muscular rigidity elicited by striatal opioid receptor stimulation

Unilateral injection of bicuculline (12.5-50 ng) into the substantia nigra pars reticulata (SNR) dose-dependently produced a tonic activity in the electromyogram (EMG), which was antagonized by coadministered muscimol. Bilateral lesions of the caudate nucleus with kainic acid failed to affect the EMG activity produced by unilateral injection of bicuculline into the SNR. Administration of muscimol (12.5 and 25 ng) into the SNR antagonized the tonic activity in the EMG produced by morphine (15 mg/kg i.p.), whereas bicuculline (50 ng) enhanced it. These results suggest that an impairment in the GABAergic neurotransmission in the SNR is relevant for mediating the tonic activity in the EMG produced by morphine and that GABAergic mechanisms in the SNR play an important role in the modulating the opioid-induced alterations in the striatal function.     

Correlation between rotational behaviors and neurochemical changes associated with damage of rat striatum: Analysis using unilateral microinjection of kainic acid

The correlation between rotational behaviors and neurochemical changes associated with the striatal damage induced by an unilateral microinjection of kainic acid were investigated. Shortly after the unilateral striatal injection of kainic acid, rats exhibited contralateral rotational behaviors, and these changes were antagonized by the simultaneous striatal injection of haloperidol. On the other hand, systemic injection of methamphetamine to animals having the lesion on nigro-striatal dopaminergic neurons exhibited ipsilateral turnings. In addition, it was found that the release of [¹⁴C]dopamine from striatal slices was increased by the in vitro addition of kainic acid. Following 2 days after the striatal injection of kainic acid and thereafter, the rats exhibited ipsilateral rotational behaviors and microinjection of muscimol into the ipsilateral substantia nigra of these animals altered turning movements to a contralateral type. Simultaneous nigral injection of bicuculline antagonized to the muscimol-induced contralateral turnings. These results suggest that the increase of dopamine release from dopaminergic neurons in the striatum may be involved in the occurrence of contralateral turning behaviors observed shortly after the striatal kainic acid treatment. The present results also suggest that changes in the functional states of striatonigral GABA-ergic neurons may play an important role in the occurrence of ipsilateral rotational movements at a late stage following the striatal injection of this agent.     

Features and mechanisms of realization the respiratory influences of the extrapyramydal system structures

In the publication the modern condition of the problem of suprabulbar regulation of breathing is analysed. The review on structure, neurochemistry and anatomic connections of the red nucleus and substantia nigra with the medullary respiratory center is submitted. The data on the respiratory effects of GABA and apomorphine microinjected into the red nucleus and substantia nigra as well as effects of their electrostimulation after the blockade of GABA and dopamine receptors in the respiratory center are discussed. The conceptual scheme of the mechanisms of realization the respiratory influences of the extrapyramydal system is offered.     

Supersensitivity of substantia nigra pars reticulata neurons to GABAergic drugs after striatal lesions

Rats were given unilateral, intrastriatal injections of kainic acid in order to destroy striatal and pallidal GABAergic projections to the substantia nigra. Two to 3 weeks after the lesions were made, a population of neurons in the substantia nigra pars reticulata was found to be significantly more sensitive to the inhibitory actions of iontophoretically appled GABA, although their responsiveness to iontophoresed glycine was not significantly altered. The increased sensitivity was reflected by a 48% decrease in the IT₅₀ value for GABA. In addition, pars reticulata cells became more sensitive to the inhibitory actions of i.v. muscimol, a GABA agonist. While the change in sensitivity was not statistically significant at 2–3 weeks, cells were markedly more sensitive to i.v. muscimol by 5–6 weeks after the lesions were made. This increased sensitivity was indicated by a 2.5 fold shift to the left in the cumulative dose-response curve and a significant decrease in the ED₅₀ value for muscimol. These results (1) demonstrate that a population of substantia nigra pars reticulata neurons becomes “functionally” supersensitive to GABAergic agents after destruction of the striatonigral GABA pathway, and (2) support the idea that these cells lie postsynaptic to striatonigral GABAergic fibers. The implications of these findings with respect to the etiology and treatment of tardive dyskinesia are discussed.     

GABA in the entopeduncular nucleus and the subthalamic nucleus participates in mediating dopaminergic striatal output functions

The bilateral intracerebral injection of the specific GABA agonists muscimol (25, 100 ng) and THIP (500 ng) into the pallido-entopeduncular nucleus (EP) and the subthalamic nucleus (STN) of rats induced a behavioural stimulation closely resembling the syndrome evoked by direct stimulation of dopamine receptors in the striatum or by the systemic injection of dopamine agonists. The rats showed strong locomotor and rearing activity followed by characteristic stereotyped behaviour consisting of sniffing and gnawing activity. The stimulation induced by muscimol (25 ng) was found independent of dopamine, since the dopamine antagonist haloperidol (1 mg/kg s.c.) induced no blockade. Injection of the GABA antogonist picrotoxin (100 ng) into the EP or STN induced sedation and catalepsy. The unilateral injection of muscimol and picrotoxin provoked contraversive and ipsiversive postural changes. Related behavioral effects were induced by GABAergic drugs injected in substantia nigra, zona reticulata (SNR). These data provide support for the new hypothesis that GABA in the EP, SNR and STN is important for the expression of behavior related to stimulation of dopamine receptors in the striatum. The effects may be induced by a dopamine activation of the descending striato-EP, striato-SNR GABAergic pathways and possibly also the pallido-STN GABAergic pathway. The findings suggest that in addition to a pathology of the dopamine system there may also be a GABAergic dysfunction in the efferent system of the basal ganglia localized to the EP, SNR and STN in diseases, such as parkinsonism, Huntington's chorea and possibly schizophrenia.     

Suppression of apomorphine-induced oral stereotypy in rats by microinjection of muscimol into midbrain

Rats with large lesions of the superior colliculus do not display the oral stereotypy normally induced by high systemic doses of dopamine-agonists. It has been suggested that collicular lesions have such an effect because they destroy the GABAergic nigrotectal pathway. This suggestion was investigated by observing the effects of bilateral microinjections of the GABA-agonist muscimol into midbrain sites in rats given 8 mg/kg subcutaneous apomorphine. A low dose of muscimol (25 ng in 0.5 ul saline/side) injected into regions of the superior colliculus with nigrotectal innervation almost abolished apomorphine-induced licking and gnawing. Control microinjections of saline into the superior colliculus, or of muscimol into overlying cerebral cortex, were ineffective. This result is consistent with the GABAergic nigrotectal projection being important for the expression of dopamine-related oral stereotypy. It was also found, however, that 25 ng of muscimol suppressed oral stereotypy when microinjected into the mesencephalic reticular formation underlying the superior colliculus. The anatomical basis of this latter effect is uncertain.     

The role of nigral projections to the thalamus in drug-induced circling behaviour in the rat

Unilateral injection of 6-hydroxydopamine (6-OHDA) into the ascending nigrostriatal pathway caused contraversive circling to apomorphine and ipsiversive circling to amphetamine respectively. An electrolesion of the ventromedial thalamic nucleus on the same side as the 6-OHDA lesion reduced apomorphine-induced circling, but not that to amphetamine. An electrolesion of the ventromedial thalamic nucleus on the side opposite to the 6-OHDA lesion reduced amphetamine circling but not that to apomorphine. Bilateral electrolesions of the ventromedial thalamic nucleus reduced neither apomorphine- nor amphetamine-induced circling. Electrolytic lesions of the parafascicular thalamic nucleus did not reduce apomorphine- or amphetamine-induced circling in animals with a unilateral 6-OHDA lesion of the nigrostriatal pathway. Knife cuts rostral and dorsal to the substantia nigra did not attenuate circling induced by injection of muscimol into the substantia nigra. Circling due to activition of nigral output pathways can be mediated by descending nigro-reticular pathways.     

Stereotyped behaviour after cholinergic, but not dopaminergic, stimulation of the substantia nigra in rats

Stereotyped behaviour of the rat was measured after intracerebral drug application in an objective and quantitative way by means of a new method developed in this laboratory. Bilateral intranigral injection of apomorphine /APO/, a specific dopaminergic agonist, did not evoke any signs of stereotyped behaviour. Also ineffective was the application of APO in the amygdaloid nucleus. Dopaminergic blockade of the substantia nigra by topical application of triperidol, a potent dopaminergic antagonist, failed to influence the stereotypy elicited by systematic APO administrationDirect cholinergic stimulation of the substantia nigra with carbachol resulted in a dose-related stereotyped behaviour not distinguishable by sight from that evoked by systematic APO administration. The effect of intranigral carbachol was antagonized by a previous intraperitoneal injection of 10 mg/kg of atropine. Stereotypy could easily be produced also by intracaudate application of APO. Topical triperidol blockade of the caudate nucleaus prevented the stereotypy caused by intraperitoneal application of APO.It is concluded that at least a part of nigral neurons cannot be directly excited by apomorphine. However, they can be excited by carbacol and seem thus, to contain muscarinic receptors. The stimulation of these receptors results in an excitation of the neurons involved and produces marked stereotyped behaviour.     

大白鼠脚内核的传入性联系

众所周知,肉食动物和大白鼠的脚内核,相当于灵长类的内侧苍白球(Nagy et al.1978;Fox and Schmitz 1944);它们的细胞形态、传入及传出均相同。早期以及近年来的一些研究工作者,虽然在研究其他核团的投射时,联系到一些本核团的传入,但是尚缺乏对本核团传人的系统研究。本实验即是应用辣根过氧化物酶的逆行传递法来研究大白鼠脚内核的传入性联系。     

Blockade of nociceptin/orphanin FQ transmission in rat substantia nigra reverses haloperidol-induced akinesia and normalizes nigral glutamate release

We recently showed that pharmacological blockade of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptors located in the substantia nigra stimulates the nigrostriatal dopaminergic pathway and motor behavior (Marti et al. J. Neurosci. 2004, 24, 6659-6666). To investigate whether such motor-stimulating action was dependent on functional dopaminergic transmission, the selective NOP receptor peptide antagonist [Nphe1,Arg14,Lys15]N/OFQ-NH2 (UFP-101) was microinjected into the substantia nigra reticulata of rats made cataleptic by systemic haloperidol administration. UFP-101 reduced haloperidol-induced akinesia as measured by immobility time in the bar test. UFP-101 also induced contralateral turning in cataleptic rats. To investigate the mechanisms involved in the anti-akinetic action of UFP-101, nigral glutamate release was monitored by microdialysis technique. The anti-akinetic action of UFP-101 correlated with normalization of nigral glutamate release, previously elevated by haloperidol injection. We conclude that endogenous N/OFQ in the substantia nigra sustains akinesia generated by impaired DA transmission and subthalamic nucleus overactivation. NOP receptor antagonists may be beneficial in the symptomatic therapy of parkinsonism, via normalization of subthalamonigral glutamatergic transmission.     

Evidence for a nigro-pulvinar-lateralis posterior complex projection in the cat using horseradish peroxidase neuronal retrograde technique

The possible existence of a direct projection from the substantia nigra to the pulvinar-lateral posterior complex (Pul-LP) was investigated in the cat by using the horseradish peroxidase technique. In particular horseradish peroxidase was injected in the Pul-LP of 8 animals, either unilaterally or bilaterally. Tissue sections obtained from the cat's brain 24-48 hrs. after injection were prepared according to Mesulam's method as slightly modified by the authors. Retrogradelly labelled neurons were observed in substantia nigra pars lateralis and reliculata ipsilaterally to the injected pulvinar-lateral posterior complex. A small number of labelled cells were also found in the contralateral substantia nigra. These findings demonstrate the existence of a close connection between two system which are involved in turning behavior: the nigrostriatal and the pulvinar-lateral posterior complex-superior colliculus.     

Behavioral and biochemical assessment of time-related changes in globus pallidus and striatal dopamine induced by intranigrally administered neurotensin

Microinjection of neurotensin (NT; 2 and 5 μg) into the substantia nigra zona compacta caused an increase in dopamine (DA) and DA metabolites in the rodent globus pallidus and striatum which persisted for at least 20 hours after peptide administration. Similar NT treatments given unilaterally into the nigra caused circling away from the injected side in amphetamine-pretreated rats, but were without effect when microinjected into saline-pretreated animals. Circling also occurred when the animals were given amphetamine 20 hours after intranigral NT administration. Contralateral rotation was observed with unilateral intranigral injections of gamma-hydroxybutyric acid (GHB; 400 μg) or with lower intranigral GHB doses (250 μg) in amphetamine-pretreated animals. The effects of GHB and NT differed in the manner in which the animals rotated as well as in the profile of DA and DA metabolite changes induced by these drugs. These studies indicated that: (1) dopaminergic functions of the globus pallidus are influenced, like the striatum, by manipulations of the substantia nigra; (2) NT and GHB likely act via different mechanisms to effect nigral dopamine-containing cells; and (3) NT was capable of inducing changes in dopamine neurons which had long term consequences.     

Feeding following microinjection of cholinergic substances into substantia nigra.

Microinjections of acetylcholine and eserine localised within the substantia nigra of the rat elicited a dose-dependent increase in feeding, but not drinking when both food and water were freely available. When required to perform an operant response for food, microinjections of carbachol into substantia nigra caused a dose-dependant increase in lever pressing for food (FR5). High doses of carbachol (1.0 and 5.0 μ1) elicited a behavioural stereotypy characterised by chewing, gnawing and biting. A significant negative correlation was found between the effectiveness of cholinergic stimulation and the distance from the site of highest feeding which was in the pars compacta region of substantia nigra. These data suggest a functional role for acetylcholine within substantia nigra and provide indirect support for the concept of an interaction between cholinergic and dopaminergic neurons within this structure.     

低频电刺激大鼠脚桥核对丘脑腹外侧核神经元自发放电的影响及其机制

本文旨在观察低频电刺激脚桥核(pedunculopontine nucleus,PPN)对帕金森病(Parkinson’s disease,PD)模型大鼠丘脑腹外侧核(ventrolateral thalamic nucleus,VL)神经元自发放电活动的影响,以探讨低频电刺激PPN改善PD症状的作用机制。通过纹状体内注射6-羟多巴胺制备PD大鼠模型。采用在体细胞外记录、电刺激及微电泳方法,观察低频电刺激PPN、微电泳乙酰胆碱(acetylcholine,ACh)及其M型受体阻断剂阿托品(atropine,ATR)、γ-氨基丁酸(γ-aminobutyric acid,GABA)及其A型受体阻断剂荷包牡丹碱(bicuculline,BIC)对大鼠VL神经元放电频率的影响。结果显示,低频电刺激PPN可使正常大鼠和PD大鼠VL神经元自发放电频率增加。微电泳ACh对VL神经元具有兴奋和抑制两种作用,而微电泳ATR则主要抑制VL神经元,即使对被ACh抑制的神经元也产生抑制作用。微电泳GABA抑制VL神经元,而微电泳BIC则兴奋VL神经元。另外,在微电泳ACh的过程中微电泳GABA,被ACh兴奋或抑制的VL神经元放电频...     

Nigro-neostriatal projection

Summary The nigro-neostriatal projection was investigated in albino rats and cats with silver impregnation, fluorescence histochemistry and electron microscopy. After unilateral stereotactic electrolysis in the substantia nigra the dopamine fluorescence of ipsilateral neostriatum is markedly reduced. As shown by silver impregnation and electron microscopy, fine terminals and axons are degenerated in the same region. These observations suggest that the nigro-neostriatal pathway may be composed of the fine dopaminergic axons of the nerve cells of unilateral substantia nigra.Dedicated to Professor K. Goerttler on his 75th birthday. — This work was supported by a research grant from the Ministry of Education, Japan.     

Protection by the NDI1 gene against neurodegeneration in a rotenone rat model of Parkinson's disease

It is widely recognized that mitochondrial dysfunction, most notably defects in the NADH-quinone oxidoreductase (complex I), is closely related to the etiology of sporadic Parkinson's disease (PD). In fact, rotenone, a complex I inhibitor, has been used for establishing PD models both in vitro and in vivo. A rat model with chronic rotenone exposure seems to reproduce pathophysiological conditions of PD more closely than acute mouse models as manifested by neuronal cell death in the substantia nigra and Lewy body-like cytosolic aggregations. Using the rotenone rat model, we investigated the protective effects of alternative NADH dehydrogenase (Ndi1) which we previously demonstrated to act as a replacement for complex I both in vitro and in vivo. A single, unilateral injection of recombinant adeno-associated virus carrying the NDI1 gene into the vicinity of the substantia nigra resulted in expression of the Ndi1 protein in the entire substantia nigra of that side. It was clear that the introduction of the Ndi1 protein in the substantia nigra rendered resistance to the deleterious effects caused by rotenone exposure as assessed by the levels of tyrosine hydroxylase and dopamine. The presence of the Ndi1 protein also prevented cell death and oxidative damage to DNA in dopaminergic neurons observed in rotenone-treated rats. Unilateral protection also led to uni-directional rotation of the rotenone-exposed rats in the behavioral test. The present study shows, for the first time, the powerful neuroprotective effect offered by the Ndi1 enzyme in a rotenone rat model of PD.     

Afferent projections from the brainstem to the area hypothalamica dorsalis: a horseradish peroxidase study in the cat

Experiments using the retrograde transport of horseradish peroxidase were performed in order to identify the cells of origin the ascending projections from different brainstem regions to the area hypothalamica dorsalis (aHd) in the cat. The afferent inputs to this area originate mainly from the midbrain and medulla oblongata regions. The main afferent source of the area hypothalamica dorsalis arises from the substantia grisea centralis, where a large number of labeled cells were observed bilaterally, although more abundant on the ipsilateral side. Substantial afferents reach the aHd from the nuclei vestibularis medialis and inferior and the formatio reticularis mesencephali. A modest number of peroxidase-labeled neurons were observed in the nuclei ruber, interpeduncularis, substantia nigra, reticularis gigantocellularis, vestibularis lateralis, cuneatus and gracilis. From the pons, the nucleus raphe magnus sends a weak projection to the aHd. These anatomical data suggest that such area could be involved in visceral, sexual, nociceptive somatosensorial, sleep-waking and motor mechanisms.