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.     

Organization and efferent projections of nucleus tegmenti pedunculopontinus pars compacta with special reference to its cholinergic aspects

In an attempt to evaluate the cellular organization and efferent projections of the nucleus tegmenti pedunculopontinus pars compacta, several experiments were performed in the rat. From measurements of neurons in the nucleus tegmenti pedunculopontinus pars compacta in Nissl-stained sections, the nucleus was observed to contain many large neurons which made it possible to demarcate this nucleus from surrounding pontomesencephalic reticular formation. Two other neuronal populations, medium and small neurons, were also seen in the nucleus tegmenti pedunculopontinus pars compacta. Detailed measurements showed that 90% by volume of all neurons in the nucleus tegmenti pedunculopontinus pars compacta were large and medium-sized neurons. After injections of [ ³H]leucine into the nucleus tegmenti pedunculopontinus pars compacta, transported label was observed in dorsally and ventrally coursing ascending fibers. The dorsally coursing fibers entered the centrolateral nucleus and centre median-parafascicular complex of the thalamus. The ventrally coursing fibers produced accumulation of silver grains in the ventral tegmental area, substantia nigra pars compacta, subthalamic nucleus, zona incerta and lateral hypothalamus. Crossed fibers of the nucleus tegmenti pedunculopontinus pars compacta were observed sparsely at the levels of the thalamus and posterior commissure, and to a greater degree through the supraoptic commissure of Meynert. Much less anterograde labeling was seen in the equivalent terminal sites on the contralateral side of the brain. By electron microscopic autoradiography major terminal sites of axons of the nucleus tegmenti pedunculopontinus pars compacta were examined in rats injected with [ ³H]leucine in the nucleus tegmenti pedunculopontinus pars compacta and later injected with horseradish peroxidase in the striatum and pallidum. Statistical data showed preferential radiolabeling of terminals forming asymmetrical synaptic contact with dendrites in the centrolateral nucleus, centre median-parafascicular complex and subthalamic nucleus. Apparent terminations in the substantia nigra pars compacta proposed in earlier studies and shown in the present light microscopic autoradiograms were not supported by this ultrastructural analysis. Several radiolabeled terminals of the asymmetrical type contacting horseradish peroxidase labeled dendrites in the thalamus confirmed direct input from the nucleus tegmenti pedunculopontinus pars compacta to the thalamostriate projection neurons. [ ³H]choline injections into the thalamus and subthalamic nucleus produced retrograde perikaryal labeling of large neurons in the nucleus tegmenti pedunculopontinus pars compacta. These neurons were unlabeled after [ ³H]choline injections in the substantia nigra. Other findings suggested retrograde transport of [ ³H]choline through cholinergic terminals as well as cholinergic fibers of passage. These data suggested a selective uptake mechanism for cholinergic fibers of passage.The results emphasize the cholinergic nature of the nucleus tegmenti pedunculopontinus pars compacta innervation of the thalamus and subthalamic nucleus. Large neurons in the nucleus tegmenti pedunculopontinus pars compacta seem responsible for this cholinergic innervation and probably provide the axon terminals making asymmetrical synapses in the thalamus and subthalamic nucleus as described above. In addition, large neurons as well as medium and small ones in the nucleus tegmenti pedunculopontinus pars compacta whose transmitters and exact destinations remain unknown send a number of axons through the supraoptic commissure of Meynert to innervate the contralateral subthalamic nucleus.     

Subthalamic nucleus efferent projection to the cerebral cortex

A direct projection from the subthalamic nucleus to the dorsal cerebral cortex has been demonstrated in the rat using a retrograde axonal transport technique. Injections of horseradish peroxidase into the cerebral cortex gave rise to retrogradely-labelled neuronal cell bodies in the ipsilateral subthalamic nucleus. Labelled cells were restricted to the lateral half of the nucleus. In addition, retrograde-labelling was observed in the rostral and caudal portions of the entopeduncular nucleus. Injections of horseradish peroxidase into the striatum underlying the cortical region receiving subthalamic efferents failed to label any subthalamic nucleus or entopeduncular nucleus neurones.These findings add the cerebral cortex to the other known projection areas (globus pallidus, substantia nigra, nucleus tegmenti pedunculopontinus) of the subthalamic nucleus and might have implications for the way in which the subthalamic nucleus influences motor activity.     

Subthalamic projection to nucleus tegmenti pedunculopontinus in the rat

A projection from the subthalamic nucleus to the nucleus tegmenti pedunculopontinus has been demonstrated in the rat using retrograde and anterograde transport of horseradish peroxidase. Small, well-localized injections of peroxidase in nucleus pedunculopontinus gave rise to retrogradely labelled cell bodies in the subthalamic nucleus. Injections of peroxidase restricted to the subthalamic nucleus gave terminal labelling in nucleus pedunculopontinus.     

Topographical organization of the brainstem afferents to the lateral posterior-pulvinar thalamic complex in the cat

Following stereotaxic injections of horseradish peroxidase in the dorsal thalamus of the cat which were restricted to the lateralis posterior-pulvinar complex, labelled neurons were found in the superficial layers of the superior colliculus and in the brainstem. The retrogradely-filled cells of the brainstem were situated principally in the nucleus tegmenti pedunculopontinus, the locus coeruleus complex, the parabrachial nuclei and the dorsal tegmental nucleus of Gudden; in each case, labelled cells were more numerous on the ipsilateral side. In addition, some scattered neurons were observed in the central grey matter, the mesencephalic reticular formation, the central superior and dorsal raphe nuclei, the cuneiform nucleus, the nucleus reticularis gigantocellularis, the nucleus praepositus hypoglossi and the oculomotor nuclei. A differential organization of these projections was observed.It is concluded that the rostrointermediate subdivision of the lateralis posterior-pulvinar complex receives most of its connections from the nucleus tegmenti pedunculopontinus, from the deep layers of the superior colliculus and from the other brainstem nuclei, while the caudal subdivision (extrageniculate visual subdivision) receives its main projection from the superficial layers of the superior colliculus. The findings may have functional implications for the role of the complex in oculomotor control.     

Topographic projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta of the cat with special reference to pallidal projections

Summary Projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta (TPC) were studied by using anterograde and retrograde tracing techniques with horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) in the cat. Following WGA-HRP injections into the medial TPC area, a substantial number of retrogradely labeled cells were seen in the entopeduncular nucleus (EP) and medial half of the substantia nigra pars reticulata (SNr), whereas following WGA-HRP injections into the lateral TPC area, labeled cells were marked in the caudal half of the globus pallidus (GP) and lateral half of the SNr. To confirm the retrograde tracing study, WGA-HRP was injected into the EP or the caudal GP, and anterograde labeling was observed in the TPC areas. Terminal labeling was located in the medail TPC area in the EP injection case, while terminal labeling was observed in the lateral TPC area in the caudal GP injection case. Projections from the striatum to the pallidal complex (the EP and the caudal GP) were also studied autoradiographically by injecting amino acids into various parts of the caudate nucleus and the putamen. Terminal labeling was distributed over the whole extent of the EP and the rostral GP following injections into the rostral striatum (the head of the caudate nucleus or the rostral part of the putamen), while terminal labeling was distributed over the caudal GP following injections into the caudal striatum (the body of the caudate nucleus or the caudal part of the putamen). From these findings, we conclude that there exists a medio-lateral topography in the projection from the basal ganglia to the TPC: The EP receives afferent projections from the rostral striatum and projects to the medial TPC area, whereas the caudal GP receives projections from the caudal striatum and sends fibers to the lateral TPC area.Abbreviations BC brachium conjunctivum - CD caudate nucleus - CP cerebral peduncle - DBC decussation of the brachium conjunctivum - EP entopeduncular nucleus - GP globus pallidus - IC internal capsule - ICo inferior colliculus - LH lateral habenular nucleus - ML medial lemniscus - PN pontine nuclei - PUT putamen - SCo superior colliculus - SI substantia innominata - SN substantia nigra - SNc substantia nigra pars compacta - SNr substantia nigra pars reticulata - STN subthalamic nucleus - TH thalamus - TPC nucleus tegmenti pedunculopontinus pars compacta     

Projections of the pallidal complex: An autoradiographic study in the cat

The efferent projections of the external pallidal segment (‘globus pallidus’), and the internal pallidal segment (entopeduncular nucleus) were studied in separate experiments in the cat by the auto-radiographic tracing method. Injections of tritiated amino acids into the external pallidal segment resulted in labelling of axon systems distributed not only to the subthalamic nucleus but also in sparser density to the nucleus reticularis thalami, the substantia nigra, the caudate nucleus, the putamen, and as yet undefined areas of the cortex. Injections of tritiated amino acids into the internal pallidal segment resulted in labelling of axon systems distributed to the ventrolateral-ventroanterior complex of the thalamus, to the centrum medianum, the lateral habenular nucleus, and the mesencephalic nucleus tegmenti pedunculopontinus, pars compacta. Less prominent termination may also occur in the parafas-cicular nucleus, the nuclei of the fields of Forel, and in the mesencephalic tegmentum rostral to the nucleus tegmenti pedunculopontinus, pars compacta.The fact that this and previous studies show that the projections of the pallidal complex are more widespread than would be expected if it was only involved in motor functions, raises questions about the functional organization of the basal ganglia. These are discussed in the following paper.     

Branched output neurons of the rat subthalamic nucleus: electrophysiological study of the synaptic effects on identified cells in the two main target nuclei, the entopeduncular nucleus and the substantia nigra

The synaptic responses of entopeduncular and nigral cells to subthalamic stimulation were studied with extracellular recording techniques in rats with and without chronic lesions. Entopeduncular output cells were identified by antidromic activation from the lateral habenula, ventral anterior thalamic nucleus and tegmenti pedunculopontine nucleus. Nigral cells projecting to superior colliculus were identified by antidromic discharge. Stimulation of the subthalamic nucleus produced a short latency suppression of spontaneous activity (10-60 ms duration) of 89% of the entopeduncular cells tested in chronically lesioned rats. Of these cells, 50% were identified as projecting to lateral habenula. On the other hand, subthalamic nucleus stimulation produced a short latency excitation of 73% of the nigral cells tested (4.16 +/- 0.07 ms). Forty-eight percent of these cells projected to superior colliculus. The subthalamic fibres which terminate in entopeduncular nucleus and substantia nigra, come from the same neuronal population since the majority, if not all, rat subthalamic neurones send branched projections to both these nuclei. Therefore, the two different types of responses recorded in these nuclei are elicited by the activation of a single neuronal population. This dual effect could be easily explained if one of the responses is mediated by local interneurones. If not, the same transmitter induces the two responses. The entopeduncular nucleus and substantia nigra which are the main target nuclei of the subthalamic nucleus, are also the only known outputs of the striatum. The subthalamic efferent cells could thus modulate the activity of the entire striatal descending output. It is noteworthy that this subthalamic control is different in entopeduncular nucleus than in substantia nigra.     

Synaptic organization of the cat entopeduncular nucleus with special reference to the relationship between the afferents to entopedunculothalamic projection neurons: An electron microscope study by a combined degeneration and horseradish peroxidase tracing technique

The synaptic organization of the feline entopeduncular nucleus was studied electron microscopically. After horseradish peroxidase injections into the ventral anterior and ventral lateral nuclear complex of the thalamus, normal axon terminals synapsing with entopedunculothalamic projection neurons were classified into four types on the basis of the size and shape of synaptic vesicles in them, and types of the postsynaptic membrane differentiation. Type I and type II axon terminals were characterized by symmetrical synaptic contacts, and large ovoid or small ovoid synaptic vesicles, respectively. Type II axon terminals were further classified into two subtypes as to their sizes: one was small (IIa), the other large (IIb). Type III and type IV axon terminals were characterized by asymmetrical synaptic contacts, and large ovoid or small ovoid synaptic vesicles, respectively.

To determine the origin of each type of terminal, electrolytic lesions of the caudate nucleus or the subthalamic nuclear region were combined with horseradish peroxidase injections into the thalamus or the subthalamic nuclear region. After electrolytic lesions of the caudate nucleus, degeneration was seen in type I axon terminals contacting entopedunculothalamic projection neurons. Following electrolysis or horseradish peroxidase injection into the subthalamic nuclear region, type IIa and type IV axon terminals showed degenerations or horseradish peroxidase labelling. Such terminals also synapsed with entopedunculothalamic projection neurons. It was demonstrated that these projection neurons relay the striatal or subthalamic inputs directly to the thalamus. After horseradish peroxidase injection into the thalamus, many labelled type II axon terminals were observed to synapse with entopedunculothalamic projection neurons. Type III axon terminals were left unchanged throughout these experiments. In addition, the entopeduncular neuron was observed to receive convergent inputs from both the caudate nucleus and probably the subthalamic nucleus. Axoaxonal synapses were also found to be involved in the synaptic triad.

These results indicate that type I axon terminals originate from the caudate nucleus, part of type IIa and type IV axon terminals originate from the subthalamic nucleus or caudal to the subthalamic nuclear region, and part of type IIa and type IIb terminals come from intrinsic axon collaterals.     

大鼠终纹床核卵圆核及其邻近区域的传出纤维联系——WGA-HRP顺行追踪法研究

本实验选用150～260g的雄性Sprague-Dawley大鼠13只,把WGA-HRP/HRP混合水溶液加压注入一侧终纹床核群前外侧区的卵圆核区域,冰冻切片,TMB法呈色后,在中枢看到顺行标记终末最密集的部位是:下丘脑后部外侧区、中央杏仁核、中脑中央灰质、臂旁核、三叉神经中脑核、蓝斑;比较多的部位是视前区、下丘脑室周区、弓状核、丘脑中线核群、内侧纽核、腹侧背盖核、脚桥背盖核、中脑网状结构、中缝背核以及迷走神经复合体;在线形中缝核、中央上核、腹侧背盖区、黑质,以及延髓中介核,也看到少量标记终末。本工作对卵圆核的传出纤维联系,进行了较全面的观察。     

Subcortical projections to the prefrontal cortex in the rat as revealed by the horseradish peroxidase technique

The sources and distribution of subcortical afferents to the anterior neocortex were investigated in the rat using the horseradish peroxidase technique. Injections into the prefrontal cortex labelled, in addition to the mediodorsal thalamic nucleus, neurons in a total of fifteen subcortical nuclei, distributed in the basal telencephalon, claustrum, amygdala, thalamus, subthalamus, hypothalamus, mesencephalon and pons. Of these, the projections from the zona incerta, the lateroposterior thalamic nucleus, and the parabrachial region of the caudal mesencephalon to the prefrontal cortex have not previously been described.Different parts of the mediodorsal thalamic nucleus project to different areas of the frontal cortex. Thus, horseradish peroxidase injections in the most ventral pregenual part of the medial cortex labelled predominantly neurons in the medial anterior and dorsomedial posterior parts of the mediodorsal nucleus; injections into the more dorsal pregenual area labelled only neurons in the lateral and ventral parts of the nucleus; injections placed supragenually labelled neurons in the dorsolateral posterior part of the nucleus; and injections into the dorsal bank of the anterior rhinal sulcus labelled neurons in the centromedial part of the nucleus.Several other subcortical nuclei had projections overlapping with that of the mediodorsal thalamic nucleus. Five different types of such overlap were distinguished: (1) cell groups labelled after horseradish peroxidase injections into one of the subfields of the projection area of the mediodorsal nucleus (defined as the prefrontal cortex), but not outside this area (parataenial nucleus of the thalamus); (2) cell groups labelled both after injection into a subfield of the projection area of the mediodorsal nucleus and after injections in a restricted area outside this area (anteromedial, ventral and laterposterior thalamic nuclei); (3) cell groups labelled after injections into all subfields of the mediodorsal nucleus projection area, but not outside this area (ventral tegmental area, basolateral nucleus of amygdala); (4) cell groups labelled after injections into any area of the anterior neocortex, including the mediodorsal nucleus projection area (parabrachial neurons of the posterior mesencephalon); (5) cell groups labelled after all neocortical injections investigated (claustrum, magnocellular nuclei of the basal forebrain, lateral hypothalamus, zona incerta, intralaminar thalamic nuclei, nuclei raphe dorsalis and centralis superior, and locus coeruleus).We can draw the following conclusions from these and related findings. First, because of the apparent overlap of projections of the mediodorsal, the anteromedial and ventral thalamic nuclei in the rat, parts of the prefrontal cortex can also be called ‘cingulate’ and ‘premotor’. Second, on the basis of projections from parts of the mediodorsal nucleus, the prefrontal cortex of the rat can be subdivided into areas corresponding to those in other species. Third, the neocortex receives afferents from a large number of subcortical cell groups outside the thalamus, distributed from the telencephalon to the pons; however, the prefrontal cortex seems to be the only neocortical area innervated by the ventral tegmental area and amygdala. Finally, neither the prefrontal cortex nor the mediodorsal thalamic nucleus receives afferents from regions directly involved in sensory and motor functions.     

The organization of nucleus tegmenti pedunculopontinus neurons projecting to basal ganglia and thalamus: a retrograde fluorescent double labeling study in the rat

The organization of nucleus tegmenti pedunculopontinus (PPN) projections to the basal ganglia and thalamus was studied in the rat by using retrograde transport of fluorescent dyes. Fast blue was injected into the substantia nigra (SN) while Nuclear yellow was delivered to one of the following nuclei: globus pallidus (GP), entopeduncular nucleus, subthalamic nucleus (STN) or parafascicular nucleus of the thalamus. Retrogradely labeled cells were observed throughout the PPN without topographical arrangement. The cells labeled from the SN outnumbered those labeled from other structures. In all cases the majority of cells were single labeled and only a few cells double labeled from SN-GP or SN-STN were found. Labeled cells were either fusiform or multipolar in shape. These data suggest that distinct PPN cells project to their basal ganglia and thalamic targets without a prominent branched organization.     

Amygdaloid projections to the mesencephalon,pons and medulla oblongata in the cat

Summary Amygdalotegmental projections were studied in 26 cats after injections of horseradish peroxidase (HRP) in the diencephalon, midbrain and lower brain stem and in 6 cats after injection of ³H-leucine in the amygdala. Following HRP injections in the posterior hypothalamus, periaqueductal gray (PAG) and tegmentum many retrogradely labeled neurons were present in the central nucleus (CE) of the amygdala, primarily ipsilaterally. Injections of HRP in the posterior hypothalamus and mesencephalon also resulted in the labeling of neurons in the basal nucleus, pars magnocellularis.Following ³H-leucine injections in CE and adjacent structures autoradiographically labeled fibers were present in the stria terminalis and ventral amygdalofugal pathways. In the mesencephalon heavily labeled fiber bundles were located lateral to the red nucleus. Labeled fibers and terminals were distributed to the mesencephalic reticular formation, substantia nigra, ventral tegmental area and PAG. In the pontine and medullary tegmentum the bulk of passing fibers was located laterally in the reticular formation. Many labeled fibers and terminals were distributed to the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus and lateral tegmental fields. Many terminals were also present in the solitary nucleus and dorsal motor nucleus of the vagus nerve.The location of the cells of origin and the distribution of the terminals of the amygdalotegmental projection suggest that this pathway plays an important role in the integration of somatic and autonomic responses associated with affective defense.Abbreviations A nucleus ambiguus - AL lateral amygdaloid nucleus - AQ cerebral aqueduct - BC brachium conjunctivum - BL basal amygdaloid nucleus, pars magnocellularis - BM basal amygdaloid nucleus, pars parvocellularis - BP brachium pontis - CE central amygdaloid nucleus - CI internal capsule - CN cochlear nucleus - CO cortical amygdaloid nucleus - CP cerebral peduncle - DCN dorsal column nuclei - DMV dorsal motor nucleus of the vagus nerve - E entopeduncular nucleus - F fornix - FLA longitudinal association bundle - GP globus pallidus - H hippocampal formation - 1C inferior colliculus - INJ injection site - LC locus coeruleus - IO inferior olive - LG lateral geniculate nucleus - LRN lateral reticular nucleus - LT lateral tegmental field - M medial amygdaloid nucleus - MB mammilary body - MG medial geniculate nucleus - ML medial lemniscus - MT medial tegmental field - MV motor nucleus of the trigeminus - OC optic chiasm - OT optic tract - P putamen - PAG periaqueductal gray - PB parabrachial nuclei - PC posterior commissure - PH posterior hypothalamus - PT pyramidal tract - PV principal sensory nucleus of the trigeminus - PYR pyriform cortex - R red nucleus - RF reticular formation - S solitary nucleus - SC nucleus subcoeruleus - SN substantia nigra - SO superior olive - SOL solitary nucleus - SPV spinal trigeminal complex - ST stria terminalis - VC vestibular complex - VTA ventral tegmental area - VII facial nucleus - XII hypoglossal nucleus     

大鼠视前内侧区的传出性神经纤维联系—WGA—HRP法研究

应用WGA-HRP顺行轴突运输研究大鼠视前内侧区传出性神经纤维投射。结果表明:视前内侧区的上行投射向嘴侧经斜角带进入外侧隔核;经髓纹进入缰核;经无名质进入杏仁前区及经终纹进入杏仁内侧核,另有标记纤维经内侧前脑束向外下行,经视束上方进入杏仁内侧核。下行投射经内侧前脑束进入下丘脑室旁核、外侧区、内侧核、后核、弓状核、乳头体前腹核和乳头体上核。继续向尾侧,标记纤维进入中脑腹侧背盖区,并投射到中缝正中核及中缝背核。     

Comparative distribution of NADPH-diaphorase activity and tyrosine hydroxylase immunoreactivity in the diencephalon and mesencephalon of the domestic chicken (Gallus domesticus)

We described the distribution of NADPH-diaphorase-containing neurons in relation to tyrosine hydroxylase immunoreactivity in the diencephalon and mesencephalon of the chicken. In the diencephalon, both markers were found in the lateral hypothalamus, dorsal hypothalamic area, hypothalamic periventricular nucleus, paraventricular nucleus and mamillary area. A close examination showed that the fine distribution of these markers differed slightly, so that they were never observed in the same neurons. In the mesencephalon, NADPH-diaphorase and tyrosine hydroxylase immunoreactivity were found in the ventral pedunculopontine area (nucleus tegmenti pedunculopontinus pars compacta, adjacent areas surrounding the quintofrontal tract and the nucleus mesencephalicus profundus ventralis), the coeruleus complex (locus coeruleus, ventral and dorsal subcoeruleus nuclei), the ventral tegmental area and the central gray. The majority of these neurons contained either diaphorase or tyrosine hydroxylase. Nevertheless, in a few cases both markers appeared to colocalize in the same neuron, typically in large perikarya of the ventral pedunculopontine area.     

Electron microscopic identification of reticulo-subthalamic axon terminals in the cat

Synaptic boutons emanating from axons of nucleus tegmenti pedunculopontinus origin were identified by electron microscopy in the neuropil of the subthalamic nucleus. Such boutons measure 1.5-3 microns, contain round synaptic vesicles and make asymmetrical axodendritic and axosomatic synaptic contacts with large subthalamic neurons. Very few contacts with vesicle-containing dendrites, and no contacts with the perikarya of the small neurons were observed. The present findings, in keeping with the relevant light microscopic and electrophysiologic data, furnish evidence for a substantial bilateral tegmenti pedunculopontinofugal projection that excites monosynaptically the relay subthalamic neurons.     

Projections from the intracerebellar nuclei to the ventral midbrain tegmentum in the rat

The present study was undertaken to provide anatomical evidence, in the rat, for a direct projection from the cerebellum towards structures, other than the red nucleus, which belong to the ventral midbrain tegmentum, by using the retrograde as well as the anterograde horseradish peroxidase transport method. Following unilateral injection in the ventral midbrain tegmentum of horseradish peroxidase, free or conjugated to wheat germ agglutinin, sparing the red nucleus, retrogradely labeled neurons were found in the contralateral cerebellar lateral nucleus and, at lower density, in the interpositus nucleus. No labeled neurons were found in the fastigial nucleus of either side. Anterogradely labeled axons from lectin coupled horseradish peroxidase injection sites in the lateral and interpositus nuclei reached the contralateral ventral midbrain tegmentum. Terminal labeling was observed in the entire red nucleus as well as in the lateral division of the ventral tegmental area of Tsai, in the dorsal region of the substantia nigra pars compacta, and in the medial part of the retrorubral field. No terminal labeling was found in the caudal linear nucleus, interfascicular nucleus, peripeduncular nucleus, rostral linear nucleus of the raphe, substantia nigra pars lateralis and the substantia nigra pars reticulata. Terminal labeling was also not observed in the ventral midbrain tegmentum following horseradish peroxidase injection in lateral and interpositus nuclei of rats pretreated with kainic acid. In conclusion, it is noteworthy that, besides the red nucleus, the sole structures of ventral midbrain tegmentum receiving cerebellar efferents are those with a higher density of dopaminergic cells.     

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.     

Organization of the efferent projections of the pedunculopontine tegmental nucleus of the midbrain of the dog pallidum

Studies of the pedunculopontinopallidal projections of the dog brain based on the retrograde axonal transport of horseradish peroxidase demonstrated that the compact zone (PPNc) and the lateral area of the diffuse zone (PPNd) of the pedunculopontine tegmental nucleus (PPN) of the midbrain project to the globus pallidus, entopeduncular nucleus, and ventral pallidum. The medial area of the PPNd, adjacent to the chiasm of the upper cerebellar peduncles and seen in other animals as the mesencephalic extrapyramidal area (MEA), projects only to the globus pallidus. In dogs, this area of the tegmentum is not a major source of projections to the striopallidum, such that it is inappropriate to regard it as a separate structure, comment being restricted to the topical organization of PPNd projections to the pallidum. Projection fibers to pallidal structures arise from both cholinergic and non-cholinergic PPN neurons. __________ Translated from Morfologiya, Vol. 127, No. 2, pp. 19–23, March–April, 2005.