帕金森病模型大鼠中脑腹侧被盖区酪氨酸羟化酶免疫阳性神经元的改变

目的探讨帕金森病(PD)模型大鼠中脑腹侧被盖区(VTA)酪氨酸羟化酶(TH)免疫阳性神经元的改变。方法将6-羟基多巴胺(6-OHDA)分别注入实验组大鼠左侧黑质致密部和中脑被盖腹侧区以建立帕金森病模型,于术后4d、7d、14d、21d、28d腹腔注射阿扑吗啡(apomorphine,APO),观察并记录大鼠行为学变化情况,利用Nissl染色、酪氨酸羟化酶(TH)免疫细胞化学染色观察大鼠中脑腹侧被盖区神经组织及TH免疫阳性神经元的改变。结果APO诱发实验组PD大鼠均向健侧(右侧)旋转,旋转启动时间逐渐缩短,持续时间逐渐延长,旋转速度逐渐加快,至术后2周旋转行为趋于稳定;Nissl染色见实验组PD大鼠损毁侧(左侧)中脑VTA区神经元数目显著减少,尼氏体模糊,颗粒及密度均降低,伴有大量胶质细胞增生,术后2周、4周注射侧神经元数目较术后1周明显减少(P<0.05);实验组PD大鼠损毁侧(左侧)中脑VTA的TH阳性神经元明显减少,神经元胞体轮廓及突起不清晰,TH阳性纤维也明显减少,分布稀疏,术后2周、4周注射侧阳性神经元数目较术后1周明显减少(P<0.05)。结论PD大鼠损毁侧中脑VTA神经组织有明显破坏,TH阳性神经元显著减少,提示中脑腹侧被盖区TH免疫阳性神经元的改变参与了PD模型大鼠的病理学变化。     

Afferents to the basal forebrain cholinergic cell area from pontomesencephalic--catecholamine, serotonin, and acetylcholine--neurons

The afferent input to the basal forebrain cholinergic neurons from the pontomesencephalic tegmentum was examined by retrograde transport of wheatgerm agglutinin-horseradish peroxidase in combination with immunohistochemistry. Multiple tyrosine hydroxylase-, dopamine-beta-hydroxylase-, serotonin- and choline acetyltransferase-immunoreactive fibres were observed in the vicinity of the choline acetyltransferase-immunoreactive cell bodies within the globus pallidus, substantia innominata and magnocellular preoptic nucleus. Micro-injections of horseradish peroxidase-conjugated wheatgerm agglutinin into this area of cholinergic perikarya led to retrograde labelling of a large population of neurons within the pontomesencephalic tegmentum, which included cells in the ventral tegmental area, substantia nigra, retrorubral field, raphe nuclei, reticular formation, pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus, parabrachial nuclei and locus coeruleus nucleus. Of the total population of retrogradely labelled neurons, a significant (approximately 25%) proportion were tyrosine hydroxylase-immunoreactive and found in the ventral tegmental area (A10), the substantia nigra (A9), the retrorubral field (A8), the raphe nuclei (dorsalis, linearis and interfascicularis) and the locus coeruleus nucleus (A6), Another important contingent (approximately 10%) was represented by serotonin neurons of the dorsal raphe nucleus (B7), the central superior nucleus (B8) and ventral tegmentum (B9). A small proportion (less than 1%) was represented by cholinergic neurons of the pedunculopontine (Ch5) and laterodorsal (Ch6) tegmental nuclei. These results demonstrate that pontomesencephalic monoamine neurons project in large numbers up to the basal forebrain cholinergic neurons and may represent a major component of the ventral tegmental pathway that forms the extra-thalamic relay from the brainstem through the basal forebrain to the cerebral cortex.     

Ascending projections of presumed dopamine-containing neurons in the ventral tegmentum of the rat as demonstrated by horseradish peroxidase

The projections of presumed dopamine-containing neurons in the zona compacta of the substantia nigra and the ventral tegmental area were examined by stereotaxic injections of horseradish peroxidase into diverse cortical and subcortical regions which are known to include dopamine-containing terminals. Neurons in the lateral half of the substantia nigra pars compacta were labelled after injections into the caudolateral aspect of the caudate-putamen, while neurons in the medial part of the substantia nigra pars compacta and lateral aspect of the ventral tegmental area projected to the anteromedial portion of the caudate putamen. Injections of horseradish peroxidase into the amygdala resulted in the appearance of reactive neurons in the anterior portion of the ventral tegmental area, but the more caudally located entorhinal cortex received projections from the posterior half of the ventral tegmental area. Injections of horseradish peroxidase into the frontal cortex, anterior to the genu, produced scattered labelled cells in the rostral half of the ventral tegmental area, whereas more posterior injections into the cingulate cortex resulted in the appearance of reactive cells which were confined to the medial one-quarter of the substantia nigra pars compacta. The near-midline structure, the lateral septum, was innervated by neurons with cell bodies primarily in the medial half of the ventral tegmental area. Injections of horseradish peroxidase into the nucleus accumbens, which contains very high levels of dopamine, resulted in the appearance of many labelled neurons throughout the ventral tegmental area and some reactive neurons in the medial part of the substantia nigra pars compacta. A few labelled cells were also occasionally observed in the contralateral ventral tegmental area after accumbens injections.These results suggest that although there is considerable overlap, and that the same subdivisions within the substantia nigra pars compacta and the ventral tegmental area appear to innervate diverse regions of the forebrain, there also exists a general topographical organization with respect to the projections of these neurons.Injections of horseradish peroxidase into some of the forebrain regions also resulted in the appearance of reactive cells in mesencephalic nuclei not known to contain dopaminergic perikarya. For example, labelled cells were observed in the supramamillary nucleus after injections into the frontal cortex, entorhinal cortex, accumbens and lateral septum. Injections into the amygdala produced reactive cells in the suprageniculate nucleus, the peripeduncular nucleus, and the magnocellular nucleus of the medial geniculate. These latter results are discussed with reference to the possibility that such pathways may mediate the responsiveness of cells in the amygdala to a wide range of sensory stimuli.     

Morphological study of the tegmental pedunculopontine nucleus, substantia nigra and subthalamic nucleus, and their interconnections in rat organotypic culture

The morphological organization of the tegmental pedunculopontine nucleus, midbrain extrapyramidal area, substantia nigra and subthalamic nucleus and their interrelationships were studied in rat organotypic culture using immunohistochemistry and NADPH-diaphorase histochemistry. Three coronal sections, one containing the tegmental pedunculopontine nucleus/midbrain extrapyramidal area, another with the substantia nigra and the third with the subthalamic nucleus, were obtained from postnatal 1-2-day-old rats. These sections were co-cultured for 3-4 weeks using the roller-tube technique. In the tegmental pedunculopontine nucleus/midbrain extrapyramidal area, the distribution pattern of cholinergic neurons was similar to that found in the in vivo study. We could, therefore, identify the subdivisions of the tegmental pedunculopontine nucleus (i.e., pars compacta and pars dissipata) and the midbrain extrapyramidal area. As in the in vivo situation, glutamate immunoreactive neurons were also located in these areas. Approximately 10% of NADPH-diaphorase positive neurons in the tegmental pedunculopontine nucleus, were glutamate immunoreactive. In the substantia nigra, as in the in vivo, tyrosine hydroxylase immunoreactive (putative dopaminergic) neurons were identified predominantly in the substantia nigra pars compacta, and parvalbumin immunoreactive neurons (putative GABAergic) mainly in the substantia nigra pars reticulata. The subthalamic nucleus was ladened with glutamate immunoreactive neurons. NADPH-diaphorase stained axons originating from the tegmental pedunculopontine nucleus were traced into the substantia nigra and subthalamic nucleus. They were often in close apposition to tyrosine hydroxylase immunoreactive neurons in the substantia nigra. Parvalbumin immunoreactive fibers from the substantia nigra projected heavily to the midbrain extrapyramidal area, but only sparsely to the tegmental pedunculopontine nucleus and the subthalamic nucleus. These findings indicate that the tegmental pedunculopontine nucleus/midbrain extrapyramidal area, substantia nigra and subthalamic nucleus in the organotypic culture have retained a basic morphological organization and connectivity similar to those seen in the in vivo situation. Therefore, this preparation could be a useful model to conduct further studies to investigate functional circuits among the structures represented.     

Organization of somatic motor inputs from the frontal lobe to the pedunculopontine tegmental nucleus in the macaque monkey

To reveal the somatotopy of the pedunculopontine tegmental nucleus that functions as a brainstem motor center, we examined the distribution patterns of corticotegmental inputs from the somatic motor areas of the frontal lobe in the macaque monkey. Based on the somatotopical map prepared by intracortical microstimulation, injections of the anterograde tracers, biotinylated dextran amine and wheat germ agglutinin-conjugated horseradish peroxidase, were made into the following motor-related areas: the primary motor cortex, the supplementary and presupplementary motor areas, the dorsal and ventral divisions of the premotor cortex, and the frontal eye field. Data obtained from the present experiments were as follows: (i) Corticotegmental inputs from orofacial, forelimb, and hindlimb representations of the primary motor cortex tended to be arranged orderly from medial to lateral in the pedunculopontine tegmental nucleus. However, the distribution areas of these inputs considerably overlapped; (ii) The major input zones from distal representations of the forelimb and hindlimb regions of the primary motor cortex were located medial to those from their proximal representations, although there was a substantial overlap between the distribution areas of distal versus proximal limb inputs; (iii) The main terminal zones from the forelimb regions of the primary motor cortex, the supplementary and presupplementary motor areas, and the dorsal and ventral divisions of the premotor cortex appeared to overlap largely in the mediolaterally middle aspect of the pedunculopontine tegmental nucleus; and (iv) Corticotegmental input from the frontal eye field was scattered over the pedunculopontine tegmental nucleus.Thus, the present results indicate that the pedunculopontine tegmental nucleus is likely to receive partly separate but essentially convergent cortical inputs not only from multiple motor-related areas representing the same body part, but also from multiple regions representing diverse body parts. This suggests that somatotopical representations are intermingled rather than segregated in the pedunculopontine tegmental nucleus.     

帕金森病模型大鼠丘脑底核及初级运动皮质放电模式的变化**

背景：以丘脑底核作为刺激靶点的脑深部刺激在治疗帕金森病上取得了良好的效果,但其治疗机制尚不明确。 目的：观察帕金森病病理状态下丘脑底核和初级运动皮质的局部场电位变化。 方法：实验组在Wistar大鼠脑黑质致密部和中脑腹侧被盖区两点注射6-羟基多巴胺建立帕金森病大鼠模型,以在脑黑质致密部和中脑腹侧被盖区两点注射生理盐水的大鼠为对照。通过植入金属电极采集两组大鼠不同状态下丘脑底核和初级运动皮质的局部场电位。 结果与结论：实验组丘脑底核放电频率整体上明显高于对照组,且放电能量高于对照组(P < 0.05)。与静止状态相比,对照组大鼠抓食运动状态下的初级运动皮质局部场电位在7~12 Hz及12~30 Hz内变化显著(P < 0.05),在30~100 Hz内变化极显著(P < 0.01),抓食过程中信号频率整体变小;实验组大鼠在两种状态下初级运动皮质局部场电位在不同频率范围内的分布变化不大,仅在30~100 Hz内差异有非常显著性意义(P < 0.01)。说明帕金森病大鼠表现为丘脑底核电活动过强,而初级运动皮质电活动受到明显抑制。     

Characterization of the extent of pontomesencephalic cholinergic neurons' projections to the thalamus: comparison with projections to midbrain dopaminergic groups

We sought to determine whether pontomesencephalic cholinergic neurons which we have been shown previously to project to the substantia nigra and ventral tegmental area also contribute to the thalamic activation projection from the pedunculopontine and laterodorsal tegmental nuclei. Retrograde tracing, immunohistochemical localization of choline acetyltransferase and statistical methods were used to determine the full extent of the cholinergic projection from the pedunculopontine and laterodorsal tegmental nuclei to the thalamus. Progressively larger Fluoro-Gold injections in to the thalamus proportionally labeled increasing numbers of pontomesencephalic cholinergic cells both ipsi- and contralaterally in the pedunculopontine and laterodorsal tegmental nuclei. Multiple large thalamic injections left only a small fraction of the ipsilateral pontomesencephalic cholinergic group unlabeled. This small remainder did not correspond to the populations which project to the substantia nigra and ventral tegmental area, thereby indicating that substantia nigra- and ventral tegmental area-projecting cholinergic neurons must also project to the thalamus. We examined whether there existed any set of cholinergic neurons in the pedunculopontine and laterodorsal tegmental nuclei which did not innervate a thalamic target. The distribution of descending projections of the pedunculopontine and laterodorsal tegmental nuclei demonstrated that the unlabeled remainder cannot correspond to a purely descending group. We also show that substance P-positive cholinergic cells in the laterodorsal tegmental nucleus project to the thalamus. Further studies demonstrated that the small population of cholinergic cells left unlabeled from the thalamus were the smallest sized cholinergic cells, and included two groups of small, light-staining cholinergic cells located in the parabrachial area and central gray, adjacent to the main pedunculopontine and laterodorsal tegmental nuclei cholinergic groups. These small cells, in contrast to thalamic-projecting cholinergic cells, did not stain positively for reduced nicotinamide adenine dinucleotide phosphate-diaphorase. Taken together, these results indicated that all of the reduced nicotinamide adenine dinucleotide phosphate diaphorase-positive/choline acetyltransferase-positive neurons of the pedunculopontine/laterodorsal tegmental nuclei ascend to innervate some portion of the thalamus, in addition to the other targets they innervate. These findings indicate that the diverse physiological and behavioral effects attributed to the activity of pontomesencephalic cholinergic neurons should not be dissociated from their activating effects in the thalamus.     

The Brainstem Pathologies of Parkinson's Disease and Dementia with Lewy Bodies

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are among the human synucleinopathies, which show alpha‐synuclein immunoreactive neuronal and/or glial aggregations and progressive neuronal loss in selected brain regions (eg, substantia nigra, ventral tegmental area, pedunculopontine nucleus). Despite several studies about brainstem pathologies in PD and DLB, there is currently no detailed information available regarding the presence of alpha‐synuclein immunoreactive inclusions (i) in the cranial nerve, precerebellar, vestibular and oculomotor brainstem nuclei and (ii) in brainstem fiber tracts and oligodendroctyes. Therefore, we analyzed the inclusion pathologies in the brainstem nuclei (Lewy bodies, LB; Lewy neurites, LN; coiled bodies, CB) and fiber tracts (LN, CB) of PD and DLB patients. As reported in previous studies, LB and LN were most prevalent in the substantia nigra, ventral tegmental area, pedunculopontine and raphe nuclei, periaqueductal gray, locus coeruleus, parabrachial nuclei, reticular formation, prepositus hypoglossal, dorsal motor vagal and solitary nuclei. Additionally we were able to demonstrate LB and LN in all cranial nerve nuclei, premotor oculomotor, precerebellar and vestibular brainstem nuclei, as well as LN in all brainstem fiber tracts. CB were present in nearly all brainstem nuclei and brainstem fiber tracts containing LB and/or LN. These findings can contribute to a large variety of less well‐explained PD and DLB symptoms (eg, gait and postural instability, impaired balance and postural reflexes, falls, ingestive and oculomotor dysfunctions) and point to the occurrence of disturbances of intra‐axonal transport processes and transneuronal spread of the underlying pathological processes of PD and DLB along anatomical pathways.     

Mesopontine rostromedial tegmental nucleus neurons projecting to the dorsal raphe and pedunculopontine tegmental nucleus: psychostimulant-elicited Fos expression and collateralization

The mesopontine rostromedial tegmental nucleus (RMTg) is a GABAergic structure in the ventral midbrain and rostral pons that, when activated, inhibits dopaminergic neurons in the ventral tegmental area and substantia nigra compacta. Additional strong outputs from the RMTg to the pedunculopontine tegmental nucleus pars dissipata, dorsal raphe nucleus, and the pontomedullary gigantocellular reticular formation were identified by anterograde tracing. RMTg neurons projecting to the ventral tegmental area express the immediate early gene Fos upon psychostimulant administration. The present study was undertaken to determine if neurons in the RMTg that project to the additional structures listed above also express Fos upon psychostimulant administration and, if so, whether single neurons in the RMTg project to more than one of these structures. We found that about 50% of RMTg neurons exhibiting retrograde labeling after injections of retrograde tracer in the dorsal raphe or pars dissipata of the pedunculopontine tegmental nucleus express Fos after acute methamphetamine exposure. Also, we observed that a significant number of RMTg neurons project both to the ventral tegmental area and one of these structures. In contrast, methamphetamine-elicited Fos expression was not observed in RMTg neurons labeled with retrograde tracer following injections into the pontomedullary reticular formation. The findings suggest that the RMTg is an integrative modulator of multiple rostrally projecting structures.     

Innervation of substantia nigra neurons by cholinergic afferents from pedunculopontine nucleus in the rat: neuroanatomical and electrophysiological evidence

Dopaminergic neurons of the substantia nigra pars compacta are excited by nicotine and acetylcholine, and possess both high-affinity nicotine binding sites and intense acetylcholinesterase activity, consistent with a cholinoceptive role. A probable source of cholinergic afferents is the pedunculopontine nucleus, which forms part of a prominent group of cholinergic perikarya located caudal to the substantia nigra in the tegmentum. Although pedunculopontine efferents, many of them cholinergic, project to the substantia nigra pars compacta, it has not been established whether they terminate in this structure. In the first experiment, which combined retrograde tracing with immunohistochemical visualization of cholinergic neurons, cholinergic cells in and around the pedunculopontine nucleus were found to send projections to the substantia nigra. This projection was almost completely ipsilateral. Subsequent experiments employed anaesthetized rats; kainate was microinfused into tegmental sites in order to stimulate local cholinergic perikarya, and concurrently, extracellular recordings were made of single dopaminergic neurons in the substantia nigra. Consistent with our anatomical findings, unilateral microinfusion of kainic acid in or near the pedunculopontine nucleus increased the firing rate of dopaminergic neurons situated remotely in the ipsilateral substantia nigra. The kainate-induced excitation of nigral dopaminergic neurons was dose-related and was prevented by intravenous administration of the centrally-acting nicotinic cholinergic antagonist mecamylamine. These results suggest that cholinergic perikarya in the vicinity of the pedunculopontine tegmental nucleus innervate dopaminergic neurons in the substantia nigra pars compacta via nicotinic receptors.     

Stimulation of the pedunculopontine tegmental nucleus in the rat produces burst firing in A9 dopaminergic neurons.

Stimulation of the medial prefrontal cortex in the rat produces events in midbrain dopaminergic neurons which resemble natural bursts, and which are closely time-locked to the stimulation, albeit with a very long latency. As a consequence, we have previously argued that such bursts are polysynaptically generated via more proximal excitatory amino acidergic afferents, arising, for example, from the pedunculopontine tegmental nucleus. In the present study, single-pulse electrical stimulation applied to this nucleus (and other sites in the rostral pons) was found to elicit responses in the majority of substantia nigra (A9) dopaminergic neurons. Responses usually consisted of long-latency, long-duration excitations or inhibition-excitations. Thirty-seven percent of responses (currents combined) elicited by stimulation of the pedunculopontine tegmental nucleus contained time-locked bursts, the bursts being embedded in the long-duration excitatory phases of excitation and inhibition-excitation responses. Stimulation sites located within 0.5 mm of the pedunculopontine tegmental nucleus were also effective at eliciting time-locked bursts (although less so than sites located in the nucleus itself), whereas more distal sites were virtually ineffective. For responses containing time-locked bursts, a higher percentage of stimulations produced a burst when the response was elicited from within the pedunculopontine tegmental nucleus than when it was elicited from outside: the bursts themselves having a very long latency (median of 96.2 ms; shorter than that of medial prefrontal cortex-induced bursts). Finally, although there was no difference in the distribution within the substantia nigra pars compacta of cells which exhibited time-locked bursting and those which did not, stimulation-induced bursts were elicited more frequently in dopaminergic neurons which were classified as "bursting" on the basis of their basal activity. The pedunculopontine tegmental nucleus appears to be a critical locus in the rostral pons for the elicitation of time-locked bursts in A9 dopaminergic neurons. Since time-locked bursts were more often elicited from cells which exhibited bursting under basal conditions, this suggests that rostral pontine sites, in particular the pedunculopontine tegmental nucleus, may play a role in the natural burst activity of dopaminergic neurons. Given that bursts in dopaminergic neurons are generated in response to primary and secondary reinforcers, the projection from the pedunculopontine tegmental nucleus could be one means by which motivationally relevant information (arising, for example, from the medial prefrontal cortex) reaches these cells.     

Electrophysiological characteristics of substantia nigra neurons in organotypic cultures: spontaneous and evoked activities

Morphological and electrophysiological characteristics of dopaminergic and non-dopaminergic neurons in the substantia nigra and their postsynaptic responses to stimulation of the tegmental pedunculopontine nucleus were studied in rat organotypic triple cultures. These cultures consisted of the subthalamic nucleus explant, ventral mesencephalic explant, inclusive of the substantia nigra and the mesopontine tegmentum explant, inclusive of the tegmental pedunculopontine nucleus, prepared from one- to two-day-old rats. Intracellular sharp and whole-cell recordings were obtained from three- to eight-week-old organotypic cultures. Recorded neurons were identified as dopaminergic and non-dopaminergic neurons with tyrosine hydroxylase immunohistochemistry. Dopaminergic neurons had long duration action potentials, prominent afterhyperpolarization, time-dependent inward and outward rectification and strong frequency adaptation. Spontaneous firing patterns varied from regular, irregular to burst firing. Non-dopaminergic neurons had short duration action potentials, in general no rectifying currents, and maintained high firing frequencies. Spontaneous firing patterns in these neurons were irregular or burst firing. Morphological analysis of the recorded neurons labeled with neurobiotin revealed that non-dopaminergic neurons had more extensive arborization of higher-order dendrites than dopaminergic neurons. Dopaminergic and non-dopaminergic neurons receive glutamatergic and cholinergic excitatory inputs from the tegmental pedunculopontine nucleus.These results indicate that morphological and electrophysiological characteristics of substantia nigra neurons in the organotypic culture are generally similar to those reported in in vitro slice and in vivo studies. However, spontaneous activities of dopamine neurons observed in the organotypic culture preparation more closely resemble those in in vivo preparation compared to in vitro preparation.     

Projections to the rostral reticular thalamic nucleus in the rat

Summary Afferent pathways to the rostral reticular thalamic nucleus (Rt) in the rat were studied using anterograde and retrograde lectin tracing techniques, with sensitive immunocytochemical methods. The analysis was carried out to further investigate previously described subregions of the reticular thalamic nucleus, which are related to subdivisions of the dorsal thalamus, in the paraventricular and midline nuclei and three segments of the mediodorsal thalamic nucleus. Cortical inputs to the rostral reticular nucleus were found from lamina VI of cingulate, orbital and infralimbic cortex. These projected with a clear topography to lateral, intermediate and medial reticular nucleus respectively. Thalamic inputs were found from lateral and central segments of the mediodorsal nucleus to the lateral and intermediate rostral reticular nucleus respectively and heavy paraventricular thalamic inputs were found to the medial reticular nucleus. In the basal forebrain, afferents were found from the vertical and horizontal limbs of the diagonal band, substantia innominata, ventral pallidum and medial globus pallidus. Brainstem projections were identified from ventrolateral periaqueductal grey and adjacent sites in the mesencephalic reticular formation, laterodorsal tegmental nucleus, pedunculopontine nucleus, medial pretectum and ventral tegmental area. The results suggest a general similarity in the organisation of some brainstem Rt afferents in rat and cat, but also show previously unsuspected inputs. Furthermore, there appear to be at least two functional subdivisions of rostral Rt which is reflected by their connections with cortex and thalamus. The studies also extend recent findings that the ventral striatum, via inputs from the paraventricular thalamic nucleus, is included in the circuitry of the rostral Rt, providing further evidence that basal ganglia may function in concert with Rt. Evidence is also outlined with regard to the possibility that rostral Rt plays a significant role in visuomotor functions.Abbreviations ac anterior commissure - aca anterior commissure, anterior - Acb accumbens nucleus - AI agranular insular cortex - AM anteromedial thalamic nucleus - AV anteroventral thalamic nucleus - BST bed nucleus of stria terminalis - Cg cingulate cortex - CG central gray - CL centrolateral thalamic nucleus - CM central medial thalamic nucleus - CPu caudate putamen - DR dorsal raphe nucleus - DTg dorsal tegmental nucleus - EP entopeduncular nucleus - f fornix - Fr2 Frontal cortex, area 2 - G gelatinosus thalamic nucleus - GP globus pallidus - Hb habenula - HDB horizontal limb of diagonal band - IAM interanterodorsal thalamic nucleus - ic internal capsule - INC interstitial nucleus of Cajal - IF interfascicular nucleus - IL infralimbic cortex - IP interpeduncular nucleus - LC locus coeruleus - LDTg laterodorsal tegmental nucleus - LH lateral hypothalamus - LHb lateral habenular nucleus - ll lateral lemniscus - LO lateral orbital cortex - LPB lateral parabrachial nucleus - MD mediodorsal thalamic nucleus - MDL mediodorsal thalamic nucleus, lateral segment - Me5 mesencephalic trigeminal nucleus - MHb medial habenular nucleus - mlf medial longitudinal fasciculus - MnR median raphe nucleus - MO medial orbital cortex - mt mammillothalamic tract - OPT olivary pretectal nucleus - pc posterior commissure - PC paracentral thalamic nucleus - PF parafascicular thalamic nucleus - PPTg pedunculopontine tegmental nucleus - PrC precommissural nucleus - PT paratenial thalamic nucleus - PV paraventricular thalamic nucleus - PVA paraventricular thalamic nucleus, anterior - R red nucleus - Re reuniens thalamic nucleus - RRF retrorubral field - Rt reticular thalamic nucleus - Scp superior cerebellar peduncle - SI substantia innominata - sm stria medullaris - SNR substantia nigra, reticular - st stria terminalis - TT tenia tecta - VL ventrolateral thalamic nucleus - VO ventral orbital cortex - VP ventral pallidum - VPL ventral posterolateral thalamic nucleus - VTA ventral tegmental area - 3 oculomotor nucleus - 3V 3rd ventricle - 4 trochlear nucleus     

Nucleus tegmenti pedunculopontinus: Efferent connections with special reference to the basal ganglia,studied in the rat by anterograde and retrograde transport of horseradish peroxidase

The efferent connections of the brain stem nucleus tegmenti pedunculopontinus were studied in the rat using the techniques of anterograde and retrograde transport of the enzyme horseradish peroxidase, laying particular emphasis on that part of pedunculopontinus which receives direct descending projections from the basal ganglia and related nuclei. In a preliminary series of experiments horseradish peroxidase was injected into either the entopeduncular nucleus or the subthalamic nucleus and, following anterograde transport of enzyme, terminal labelling was identified in nucleus tegmenti pedunculopontinus, surrounding the brachium conjunctivum in the caudal mesencephalon.In a subsequent series of experiments, horseradish peroxidase was injected into that region of nucleus tegmenti pedunculopontinus which receives entopeduncular and subthalamic efferents and its efferent projections were studied by anterograde transport of the enzyme. The results indicate that nucleus tegmenti pedunculopontinus gives rise to widely distributed efferent projections which terminate rostrally in mesencephalic, diencephalic and telencephalic structures and caudally in the pontine tegmentum. In the mesencephalon, terminal labelling was found in the pars compacta of the ipsilateral substantia nigra and sometimes in the adjoining ventral tegmental area. Labelling was also found in the ipsilateral half of the periaqueductal grey. In the diencephalon terminal labelling occurred bilaterally in the subthalamic nucleus and ipsilaterally in the intralaminar nuclei of the thalamus. Further rostrally, terminal labelling was particularly evident in the ipsilateral pallidal complex, especially in the caudal two-thirds of the entopeduncular nucleus and the ventral half of the caudal third of the globus pallidus. Caudal to pedunculopontine injection sites dense labelling was observed in the reticular formation of the pontine tegmentum.In a final series of experiments, confirmation of apparent pedunculopontine efferent projections was sought using the retrograde transport of horseradish peroxidase. Enzyme was injected into sites possibly receiving pedunculopontine efferents and the peribrachial area of the brain stem was examined for retrograde cell labelling. In this way, pedunculopontine projections were confirmed to the globus pallidus, entopeduncular nucleus, subthalamic nucleus, substantia nigra, parafascicular nucleus and pontine reticular formation. Injections into the globus pallidus or subthalamic nucleus gave rise to retrograde cell labelling bilaterally in pedunculopontinus. In addition, retrograde transport studies alone demonstrated projections from pedunculopontinus to the cerebral cortex and to the spinal cord.It is concluded that the nucleus tegmenti pedunculopontinus has reciprocal relationships with parts of the basal ganglia and some functionally related nuclei (in particular, the pallidal complex, subthalamic nucleus and substantia nigra). These connections support the view that nucleus tegmenti pedunculopontinus is likely to be involved in the subcortical regulation and mediation of basal ganglia influences upon the lower motor system. This suggests a potential role for pedunculopontine afferent and efferent pathways in the pathophysiology of basal ganglia related disorders of movement.     

c-Fos expression after deep brain stimulation of the pedunculopontine tegmental nucleus in the rat 6-hydroxydopamine Parkinson model

Deep brain stimulation (DBS) is used to alleviate motor dysfunction in Parkinson's disease (PD). The pedunculopontine nucleus (PPN) may be a potential target for severe freezing and postural instability with 25 Hz stimulation being considered more effective than 130 Hz stimulation. Here we evaluated the expression of c-Fos after 25 Hz and 130 Hz DBS of the pedunculopontine tegmental nucleus (PPTg, i.e., the rodent equivalent to the human PPN) in the rat 6-hydroxydopamine (6-OHDA) PD model.Anaesthetized male Sprague Dawley rats with unilateral 6-OHDA-induced nigrostriatal lesions were stimulated with 25 Hz, 130 Hz, or 0 Hz sham-stimulation for 4 h by electrodes implanted into the ipsilateral PPTg. Thereafter the distribution and number of neurons expressing the immediate early gene c-Fos, a marker for acute neuronal activity, was assessed.DBS of the PPTg induced strong ipsilateral c-Fos expression at the stimulation site, with 25 Hz having a more marked impact than 130 Hz. Additionally, c-Fos was strongly expressed in the central gray. In the dorsal part expression was stronger after 25 Hz stimulation, while in the medial and ventral part there was no difference between 25 Hz and 130 Hz stimulation. Expression in the basal ganglia was negligible.In the rat 6-OHDA PD model stimulation of the PPTg did not affect c-Fos expression in the basal ganglia, but had a strong impact on other functional circuitries. PPN stimulation in humans might therefore also have an impact on other systems than the motor system.     

The pedunculopontine tegmental nucleus and the role of cholinergic neurons in nicotine self-administration in the rat: a correlative neuroanatomical and behavioral study

The objective of this study was to determine whether the pedunculopontine tegmental nucleus plays a role in the maintenance of nicotine self-administration, and whether the ascending cholinergic projection from this nucleus to midbrain dopamine neurons in the ventral tegmental area might be involved. Studies were done with rats trained to self-administer nicotine intravenously. Self-administration was examined before and after the pedunculopontine tegmental nucleus was lesioned with the ethylcholine mustard aziridinium ion, a selective cholinergic toxin. Lesions were assessed qualitatively and quantitatively in histological sections stained for either nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry to identify cholinergic neurons, or for Nissl. Self-administration was also tested after an acute manipulation in which microinfusions of the nicotinic cholinergic antagonist dihydro-beta-erythroidine were made into the pedunculopontine tegmentum.Infusions of neurotoxin into the pedunculopontine tegmentum reduced nicotine self-administration behaviour when tested weeks later. Toxin treatment reduced the number of cholinergic neurons in the tegmentum, while largely sparing the non-cholinergic population in this area. Lesions were limited to the pedunculopontine area and did not extend to the neighboring laterodorsal tegmental nucleus or to the substantia nigra. Acute manipulation of the pedunculopontine tegmental nucleus with microinfusions of dihydro-beta-erythroidine also produced an attenuation of nicotine self-administration.Collectively these data show that the pedunculopontine tegmental nucleus is part of the neuronal circuitry mediating nicotine self-administration, and that the population of cholinergic neurons is likely a critical element.     

Is there a non-dopaminergic nigrostriatal pathway?

Sixteen per cent of the substantia nigra cell bodies normally labeled from the injection of a fluorescent retrograde tracer in the caudate-putamen complex could still be labeled by the same procedure after multiple intracisternal 6-hydroxydopamine treatments that depleted dopamine levels in the caudate-putamen complex to 1.0% of control. However, the demonstration of glyoxylic-acid-induced catecholamine histofluorescence in tissue from these lesioned rats revealed that many of the surviving retrogradely-labeled substantia nigra cell bodies still contained dopamine. The persistence of some dopamine in the substantia nigra of the lesioned animals was confirmed biochemically. Therefore, retrograde tracing in 6-hydroxydopamine lesioned rats overestimated the extent of the non-dopaminergic nigrostriatal tract.The simultaneous combination of retrograde fluorescent tracing and catecholamine histofluorescence in unlesioned animals revealed that only 5% or less of the substantia nigra cell bodies retrogradelylabeled from the caudate-putamen complex were without catecholamine fluorescence. These apparently non-dopaminergic nigrostriatal cells were located primarily in the ventral tegmental area, substantia nigra pars reticulata and extreme medial edge of the substantia nigra pars compacta.     

Biochemical evidence for γ-aminobutyrate containing fibres from the nucleus accumbens to the substantia nigra and ventral tegmental area in the rat

Glutamate decarboxylase activity, a specific marker for γ-aminobutyrate-containing neurons, has been analysed in microdissected samples from rat mesencephalon following unilateral electrocoagulations of the nucleus accumbens. This lesion resulted in a consistent decrease of 50% in the enzyme activity in the rostromedial substantia nigra, and a slight, but insignificant decrease (?15%) in the medial parts of the caudal pars compacta of the substantia nigra. No change was found in the lateral pars compacta or the central pars reticulata. In the ventral tegmental area, the highest activity was found in the rostromedial part, adjacent to the mammillary body. At this level, a significant decrease of 20% was found in the ventral tegmental area on the lesioned side. In contrast, the activities in the medial accessory optic nucleus and the caudal ventral tegmental area adjacent to the interpenduncular nucleus were unchanged.The results indicate that the nucleus accumbens sends γ-aminobutyrate-containing fibres to the rostromedial substantia nigra and to the rostral ventral tegmental area. The caudal ventral tegmental area, the lateral pars compacta and the central pars reticulata do not receive measurable amounts of such fibres.     

Excitotoxic lesions of the pedunculopontine tegmental nucleus disinhibit orofacial behaviours stimulated by microinjections of d-amphetamine into rat ventrolateral caudate-putamen

Data are presented which support the hypothesis that the pedunculopontine tegmental nucleus serves as an output station for the striatum and, in particular, has a role in the expression of behaviour stimulated from the ventrolateral caudate-putamen, a rodent homologue of the primate putamen. Rats received either bilateral ibotenate or sham lesions in the pedunculopontine tegmental nucleus and bilateral cannulation of the ventrolateral caudate-putamen. Oral motor activities were observed following microinjection of 5.0, 10.0 and 20.0 g d-amphetamine (and vehicle-only control) into the ventrolateral caudate-putamen. As expected, orofacial behaviours such as biting and licking were observed in sham-lesioned rats following this treatment, but pedunculopontine tegmental nucleus-lesioned rats exhibited an increase in the incidence of these oral motor behaviours at all doses of amphetamine compared with the controls. This increase was the product of changes in the duration and number of times in which they engaged in oral motor behaviours, but not the latency to initiate them. There was no change in the normal oral motor activities associated with grooming. Histological analysis showed that ibotenate lesions destroyed both cholinergic and non-cholinergic neurones in the pedunculopontine tegmental nucleus. These data indicate that loss of the pedunculopontine tegmental nucleus disinhibits oral motor behaviours stimulated from the ventrolateral caudateputamen by d-amphetamine and are discussed in terms of their implications for understanding the relationships between striatal outflow and structures in the pons.     

Excitatory amino acid projections to the nucleus accumbens septi in the rat: a retrograde transport study utilizing D[3H]aspartate and [3H]GABA

Afferents to the nucleus accumbens septi utilizing glutamate or aspartate have been investigated in the rat by autoradiography following injection and retrograde transport of D[3H]aspartate. Parallel experiments with the intra-accumbal injection of [3H]GABA were employed to establish the transmitter-selective nature of the retrograde labelling found with D[3H]aspartate. The topography of cortical and thalamic perikarya labelled by D[3H]aspartate was extremely precise. D[3H]Aspartate labelled perikarya were found in layer V of agranular insular cortex; bilaterally within prelimbic and infralimbic subareas perikarya, but predominantly ipsilaterally. Ipsilateral labelling was observed in dorsal, ventral and posterior agranular insular cortices, and in perirhinal cortex. Injections into ventral accumbens labelled perikarya in ipsilateral entorhinal cortex, while infusion of D[3H]aspartate into anterior caudate-putamen resulted in labelling of perikarya in ipsilateral cingulate and lateral precentral cortices. Following infusion of D[3H]aspartate, ipsilateral midline thalamic nuclei contained the highest density of labelled perikarya; infusions centred on nucleus accumbens resulted in heavy retrograde labelling of the parataenial nucleus, but labelling was sparse from a lateral site and not observed after injection into anterior caudate-putamen. Less prominent labelling of perikarya was seen in other thalamic nuclei (mediodorsal, central medial, rhomboid, reuniens and centrolateral), mostly near the midline. Perikaryal labelling was also found in the ipsilateral amygdaloid complex, particularly in basolateral and lateral nuclei. Only weak labelling resulted in ventral subiculum. Numerous labelled cells were present bilaterally in anterior olfactory nucleus, although perikarya were more prominent ipsilaterally. Labelled perikarya were not consistently observed in other regions (ventral tegmental area, medial substantia nigra, raphe nuclei and locus coeruleus) known to innervate nucleus accumbens. Presumptive anterograde labelling was detected in ventral pallidum/substantia innominata, ventral tegmental area and medial substantia nigra. [3H]GABA was generally not retrogradely transported to the same regions labelled by D[3H]aspartate; an exception being the anterior olfactory nucleus, where large numbers of labelled perikarya were found. [3H]GABA failed to label perikarya in thalamus and amygdala, and a topographic distribution of label was absent in neocortex.(ABSTRACT TRUNCATED AT 400 WORDS)