Chemical organization of projection neurons in the rat accumbens nucleus and olfactory tubercle

Projection neurons in the ventral striatum, the accumbens nucleus and olfactory tubercle, were examined by combining the retrograde tracing method and immunocytochemistry with antibodies against C-terminals of the preprodynorphin (PPD), preproenkephalin (PPE), preprotachykinin A (PPTA) and preprotachykinin B (PPTB). When the retrograde tracer was injected into the ventral pallidum, about 60% and 40% of retrogradely labeled neurons in the accumbens nucleus were immunoreactive for PPD and PPE, respectively. In contrast, all accumbens nucleus neurons projecting to the ventral mesencephalic regions including the substantia nigra and ventral tegmental area were immunopositive for PPD but not for PPE. Although no olfactory tubercle neurons projected fibers to the mesencephalic regions, 60% and 40% of olfactory tubercle neurons projecting to the ventrolateral portion of the ventral pallidum were immunoreactive for PPD and PPE, respectively, as were the accumbens nucleus neurons. About 70% of accumbens nucleus and olfactory tubercle neurons projecting to the ventral pallidum and all accumbens nucleus neurons projecting to the ventral mesencephalic regions showed PPTA immunoreactivity. A small population (2-12%) of accumbens neurons projecting to the ventral pallidum and mesencephalic regions displayed immunoreactivity for PPTB. Compared with the dorsal striatopallidal projection neurons that were reported to mostly express PPE, it was characteristic of the ventral striatum that only the smaller population (about 40%) of ventral striatopallidal projection neurons expressed PPE. This suggests that the ventral striatopallidal projection system is less specialized than the dorsal striatopallidal system in terms of peptide production, or that the ventral pallidum should be compared with a combined region of the globus pallidus and entopeduncular nucleus in the dorsal system.     

The basal forebrain projection to the region of the nuclei gemini in the rat; a combined light and electron microscopic study employing horseradish peroxidase, fluorescent tracers and Phaseolus vulgaris-leucoagglutinin

We have examined the location of basal forebrain cells projecting to the region of the nuclei gemini in the caudolateral hypothalamus of the rat using retrograde transport of wheatgerm agglutinin-horseradish peroxidase. Since many tracer-positive neurons were identified in ventral pallidal areas known to project to the mediodorsal nucleus of the thalamus, we also prepared several animals with wheatgerm agglutinin-horseradish peroxidase injections in mediodorsal thalamus. Many of the sections from both groups of animals were subsequently prepared for the demonstration of ventral pallidal regions, using either substance P or glutamate decarboxylase as a pallidal marker. Some animals received injections of different retrogradely transported fluorescent tracers in the mediodorsal thalamus and the nuclei gemini for the purpose of studying potential axon collateralization. The large gemini-projecting cells are diffusely scattered within the medial forebrain bundle area, from the caudal margin of the nucleus of the horizontal limb of the diagonal band to the rostral tip of the olfactory tubercle, and with a concentration of cells in the lateral part of the medial forebrain bundle region. Gemini-projecting cells were not found in the olfactory tubercle proper, including the islands of Calleja complexes, or in the ventral pallidal areas located dorsal to the medial forebrain bundle area underneath the lateral extension of the anterior commissure. Gemini-projecting cells within ventral pallidal areas were observed only in regions where the longitudinal fascicles of the medial forebrain bundle interdigitate with the rostroventral extension of the ventral pallidum. Anterogradely-labeled fiber plexuses in the region of the nuclei gemini were observed following injection of Phaseolus vulgaris-leucoagglutinin or Fluoro-Ruby into the forebrain regions containing retrogradely-labeled neurons following nuclei gemini injections of wheatgerm agglutinin-horseradish peroxidase. We found no evidence of cells with axonal projections to both mediodorsal thalamus and nuclei gemini. The gemini-projecting cells are generally large, triangular and plump, and the electron microscopic picture of gemini-projecting neurons is the same regardless of whether the cells are located in pallidal or non-pallidal areas.     

Ramifications of the globus pallidus in the rat as indicated by patterns of immunohistochemistry

An attempt has been made to redefine the borders of the globus pallidus by the aid of the unique pattern of enkephalin-like and substance P-like immunoreactivity characterizing the pallidum of both monkey and rat. In preparations immunoreacted for these two peptides by the peroxidase-antiperoxidase histochemical method of Sternberger this pattern appears in the form of ribbon-like fibers (here called "woolly fibers") that have been interpreted by Haber and Elde as unstained pallidal elements (dendrites and cell bodies) each enmeshed by a plexus of thin, enkephalin- or substance P-positive striatopallidal fibers. A dense enkephalin-positive woolly-fiber plexus fills the entire external pallidal segment as conventionally defined (here called "dorsal pallidum") and extends from there in various, generally ventral, directions. The most massive, rostral extension defines the subcommissural or "ventral pallidum" of Heimer and Wilson and expands from there ventraward into the olfactory tubercle, supporting Heimer's suggestion that many of the large cells of the tubercle are pallidal neurons. Further extensions from the enkephalin-positive dorsal pallidum plexus invade the ventral striatal region (including the nucleus accumbens), a dorsal region of the amygdala, and the bed nucleus of the stria terminalis. Substance P-positive woolly fibers, like their enkephalin-positive counterparts, fill the ventral pallidum and invade the olfactory tubercle, but avoid all except a small rostroventral part of the dorsal pallidum, and do not invade the striatum, the amygdala, or the bed nucleus of the stria terminalis. On the other hand, the dense substance P-positive woolly-fiber plexus filling the internal pallidal segment (entopeduncular nucleus) expands medialward into the lateral hypothalamic region. The entopeduncular nucleus invades the hypothalamus also with a loose plexus of enkephalin-positive woolly fibers. It is suggested that woolly fibers extending outward beyond the conventionally recognized borders of the pallidum represent pallidal elements innervated by enkephalin or substance P-positive fibers arising from ventromedial striatal regions in turn innervated by limbic structures.     

Comparison of the rat dorsal and ventral striatopallidal system A study using the GABAA-receptor α1-subunit and parvalbumin immunolabeling

The ventral striatum is more closely related to limbic brain regions than the dorsal striatum in spite of the remarkable similarities in the structural organization between these two brain regions. The present study is focused on the comparison of ventral striatopallidal territories and the dorsal striatopallidal system regarding the GABA_A-receptor α₁-subunit and parvalbumin immunoreactivity, as these markers showed specific distribution patterns and coexpression sites in the more intensely studied dorsal regions. Our investigations revealed that: (1) Parvalbumin single-labeled cells and a moderate number of neurons single-labeled with the GABA_A-receptor α₁-subunit exist not only in the dorsal but also in the ventral striatum, including the striatal cell bridges. In addition, morphologically similar neurons positive for the α₁-subunit were also found in the corpus callosum and anterior commissure. (2) A small number of double-labeled neurons was seen not only in dorsal but also in ventral striatal regions. Such cells were mainly located near the border with the globus pallidus and ventral pallidum. They are likely to represent a further type of striatal neuron. (3) The vast majority of neurons in the entopeduncular nucleus, the homologue of the primate internal globus pallidus segment, coexpressed α₁-subunit and parvalbumin immunoreactivity, as reported previously for the other pallidal compartments. (4) The islands of Calleja adjoining the ventral pallidal extensions in the olfactory tubercle exhibited a strong α₁-subunit immunoreactivity in the neuropil as well as somata single- or double-labeled for both markers. Our findings indicate that the dorsal and ventral striatopallidal compartments are similarly organized in general with respect to the occurrence and distribution of single- and double-labeled parvalbumin-immunoreactive and GABA_A-receptor α₁-subunit-immunoreactive neurons.     

An immunohistochemical study of somatostatin and neurotensin positive neurons in the septal nuclei of the rat brain

Summary Antibodies to the neuropeptides somatostatin (SOM) and neurotensin were used to study the distribution of the two peptides within the septum of the rat brain. In colchicine treated rats, numerous somatostatin-positive cell bodies were found in the dorsal and ventral subdivisions of the alteral septum, along the border of the nucleus accumbens, in the ventral tip of the horizontal limb of the diagonal band of Broca as well as in the anterior hippocampal rudiment, infralimbic area and several other structures of the basal forebrain (e.g., nucleus accumbens, olfactory tubercle and substantia innominata). Cell bodies containing immunoreactivity for neurotensin were situated in the intermediate and ventral subdivisions of the lateral septum, the medial septal nucleus, the diagonal band of Broca, the rostro-medial continuation of the substantia innominata and the olfactory tubercle.In untreated rats, somatostatin positive processes formed terminal plexuses in the medial septal nucleus and along an area close to the ventricular wall of the lateral ceptal nucleus. Other septal nuclei, such as the diagonal band of Broca contained a sparse innervation by somatostatin positive fibers. In contrast, the nucleus accumbens olfactory tubercle, and the substantia innominata contained a rich innervation by somatostatin positive axons and terminals. Within these structures the density of SOM positive processes show great variations with patches of densely packed terminals separated by areas of sparser or no innervation. The neurotensin positive terminals were situated predominantly within the intermediate part of the lateral septum and the medial septal nucleus. Both of these regions contained numerous pericellular baskets of neurotensin positive terminals around septal neurons. In addition to the septal innervation, several of the basal forebrain structures were rich in neurotensin positive processes with the densest innervation found in the nucleus accumbens and substantia innominata. Like the SOM-immunoreactivity distinct islands of dense neurotensin innervation separated by less or no innervation occur throughout the basal forebrain. Taken together, these findings suggest that somatostatin and neurotensin occur in separate neuronal populations and that each may influence important physiological functions within the individual septal nuclei.     

Distribution of DARPP-32 in the basal ganglia: an electron microscopic study

Summary DARPP-32, a dopamine and cyclic AMP-regulated phosphoprotein, has been studied by light and electron microscopical immunocytochemistry in the rat caudatoputamen, globus pallidus and substantia nigra. In the caudatoputamen, DARPP-32 was present in neurons of the medium-sized spiny type. Immunoreactivity for DARPP-32 was present in dendritic spines, dendrites, perikaryal cytoplasm, most but not all nuclei, axons and a small number of axon terminals. Immunoreactive axon terminals in the caudatoputamen formed symmetrical synapses with immunolabelled dendritic shafts or somata. Neurons having indented nuclei were never immunoreactive. In the globus pallidus and substantia nigra pars reticulata, DARPP-32 was present in myelinated and unmyelinated axons and in axon terminals. The labelled axon terminals in these regions formed symmetrical synaptic contacts on unlabelled dendritic shafts or on unlabelled somata. These data suggest that DARPP-32 is present in striatal neurons of the medium-sized spiny type and that these DARPP-32-immunoreactive neurons form symmetrical synapses on target neurons in the globus pallidus and substantia nigra. The presence of DARPP-32 in these striatal neurons and in their axon terminals suggests that DARPP-32 mediates part of the response of medium-size spiny neurons in the striaturn to dopamine D-l receptor activation.     

The striatal mosaic in primates: patterns of neuropeptide immunoreactivity differentiate the ventral striatum from the dorsal striatum.

Patterns of immunoreactivity for calcium-binding protein, tyrosine hydroxylase and four neuropeptides in the ventral striatum (nucleus accumbens, olfactory tubercle and ventromedial parts of the caudate nucleus and putamen) were compared to patterns of these markers in the dorsal striatum (the majority of the neostriatum) in rhesus monkey. The striatal mosaic was delineated by calcium-binding protein and tyrosine hydroxylase immunoreactivities. Both markers were found preferentially in the matrix of the dorsal striatum. The mosaic configurations of tyrosine hydroxylase, but not calcium-binding protein immunoreactivity, were similar in dorsal and ventral striatal regions. Substance P and leucine-enkephalin were not distributed homogeneously; distinct types and the prevalence of patches of substance P and leucine-enkephalin immunoreactivity distinguish the dorsal striatum from the ventral striatum and distinguish the caudate nucleus from the putamen. In the dorsal striatum, substance P and leucine-enkephalin patches consist of dense islands of immunoreactive neurons and puncta or clusters of immunoreactive neurons marginated by a dense rim of terminal-like puncta; the matrix was also enriched in leucine-enkephalin-immunoreactive neurons but contained less substance P-immunoreactive neurons. Patches were more prominent in the caudate nucleus than in the putamen. In the caudate, compartments low in tyrosine hydroxylase and calcium-binding protein immunoreactivities corresponded to cytologically identified cell islands and to patches enriched in substance P and leucine-enkephalin. These patches had a discrete infrastructure based on the location of substance P and leucine-enkephalin-immunoreactive neurons and terminals. In the ventral striatum, patches that showed low levels of substance P and leucine-enkephalin immunoreactivities were embedded in a matrix rich in immunoreactive cell bodies, fibers and terminals. In the accumbens, regions showing little tyrosine hydroxylase were in spatial register with patches low in substance P and leucine-enkephalin. Neurotensin- and somatostatin-immunoreactive neurons or processes were also compartmentally organized, particularly in the ventral striatum. Neurotensin-immunoreactive neurons were present predominantly in the nucleus accumbens but not in the dorsal striatum. Some regions enriched in neurotensin immunoreactivity were spatially registered with zones low in tyrosine hydroxylase, substance P and zones enriched in leucine-enkephalin. Areas enriched in somatostatin-immunoreactive processes overlapped with both tyrosine hydroxylase-rich and -poor regions in the ventral striatum. Our results show that the chemoarchitectonic topography of the striatal mosaic is different in the dorsal and ventral striatum of rhesus monkey and that the compartmental organization of some neurotransmitters/neuropeptides in the ventral striatum is variable and not as easily divisible into conventional patch and matrix regions as in the dorsal striatum.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunocytochemical localization of choline acetyltransferase in rat ventral striatum: a light and electron microscopic study

Summary The ventral striatum, previously defined as including the nucleus accumbens, substriatal grey, olfactory tubercle and striatal cell bridges has been examined in an immunocytochemical study with monoclonal antibodies to choline acetyltransferase (ChAT) in order to identify putative cholinergic neurons and synaptic junctions within the region. Light microscopy revealed ChAT-positive neurons with similar morphological characteristics in all divisions of ventral striatum. The somata of immunoreactive neurons were round or elongated in shape, approximately 10 × 21 m in size and had two to four dendrites that coursed long distances and occasionally branched. Electron microscopy of ChAT-positive neurons in substriatal grey initially studied by light microscopy revealed that unlabelled boutons occasionally formed synapses with immunoreactive somata and proximal dendrites, but were more numerous along distal dendrites. Light microscopy demonstrated that ventral striatal neuropil contained numerous ChAT-positive fibres and punctate structures that varied in concentration from moderate to very dense. The lateral border of the substriatal grey and the area within, and adjacent to, all islands of Calleja exhibited the most dense ChAT-positive punctate staining. Additionally, the medial portion of nucleus accumbens was more densely ChAT-positive than the lateral, and the olfactory tubercle displayed laminar variations of immunoreaction product. Counterstained immunocytochemical specimens demonstrated that some areas of dense ChAT-positive punctate staining were associated with clusters of ChAT-negative, medium-sized neurons. Furthermore, electron microscopic observations of substriatal grey revealed that ChAT-positive dense regions were associated with numerous immunoreactive boutons, some of which established synapses with unlabelled somata, dendritic shafts and spines. These results suggest that the densely ChAT-positive neuropil areas within ventral striatum receive more cholinergic innervation than the more lightly stained neuropil areas. There are numerous similarities in the morphological characteristics of ChAT-positive neurons and synapses observed in ventral striatum when compared with those previously described in dorsal striatum. However, some differences were observed, such as smaller somal sizes in ventral, as contrasted with dorsal striatum, and a substantial variation in ChAT-positive fibre and punctate neuropil staining seen within the ventral but not the dorsal striatum. Such differences suggest that the ventral striatum may exhibit greater heterogeneity of cholinergic function than the dorsal striatum.     

An electrophysiological study of the neural projections from the hippocampus to the ventral pallidum and the subpallidal areas by way of the nucleus accumbens

The integrative role of the ventral striatum in transmitting signals from the hippocampus to the ventral pallidal and subpallidal areas was investigated in urethane-anaesthetized rats using an extracellular single-unit recording technique. Neurones of the nucleus accumbens were first activated by single-pulse stimulation of the ventral subiculum of the hippocampus. Further tests were made to investigate whether these accumbens neurones could be activated antidromically by stimulation of either the ventral pallidal or subpallidal areas. More than 4 times as many accumbens neurones, activated by hippocampal stimulation, responded antidromically to stimulation of subcommissural ventral pallidum than to stimulation of the sublenticular subpallidal area. This observation suggests that the hippocampus has preferential inputs to accumbens efferent neurones which project monosynaptically to the ventral pallidum. Spontaneously active neurones in the ventral pallidum and subpallidal area were inhibited by stimulation of the ventral subiculum of the hippocampus. These inhibitory responses were reduced when glutamic acid diethyl ester, a glutamate antagonist, was microinjected into the medial accumbens, apparently blocking the hippocampal-accumbens glutamatergic synapses to both the ventral pallidal-directed and the subpallidal-directed accumbens efferents. This evidence suggests that signals from the hippocampus reach ventral pallidal and subpallidal regions by way of the nucleus accumbens. The presence of a projection from ventral pallidal and subpallidal regions to the brainstem mesencephalic locomotor region further supports the hypothesis that limbic (e.g. hippocampus) can influence somatomotor activities by way of the nucleus accumbens and its efferent projection to ventral pallidal and subpallidal regions.     

Organization of afferents to the striatopallidal systems in the fire-bellied toad Bombina orientalis

The cerebral hemispheres of amphibians display paired dorsal and ventral striatum (commonly referred to as striatum proper and nucleus accumbens, respectively). Each striatal region is proposed to be closely associated with a pallidal structure located caudal to it to form a striatopallidal system. In the present study, afferents to the dorsal and ventral striatopallidal systems of the fire-bellied toad (Bombina orientalis) were investigated using the neuronal tracer biocytin. A quantitative analysis of the topographical distribution of afferent neurons from the thalamus and posterior tubercle/ventral tegmentum was emphasised. The main results show that inputs to the two striatopallidal systems originate from distinct dorsal thalamic nuclei, with dorsal and ventral striatopallidal afferent neurons favouring strongly the lateral/central and anterior thalamic nuclei, respectively. However, afferent neuron distribution in the dorsal thalamus does not differ in the rostrocaudal axis of the brain. Afferent neurons from the posterior tubercle and ventral tegmentum, on the other hand, are organised topographically along the rostrocaudal axis. About 85 % of afferent neurons to the dorsal striatopallidal system are located rostrally in the posterior tubercle, while 75 % of afferent neurons to the ventral striatopallidal system are found more caudally in the ventral tegmentum. This difference is statistically significant and confirms the presence of distinct mesostriatal pathways in an amphibian. These findings demonstrate that an amphibian brain displays striatopallidal systems integrating parallel streams of sensory information potentially under the influence of distinct ascending mesostriatal pathways.     

The ventral striatopallidal parts of the basal ganglia in the rat--II. Compartmentation of ventral pallidal efferents

This paper describes the results of experiments designed to address whether neuron populations giving rise to different ventral pallidal efferent projections are segregated in a manner concordant with the recently described immunohistochemical compartmentation of ventral pallidum. The retrograde transport of horseradish peroxidase conjugated to wheatgerm agglutinin following injections in the ventral tegmental area of Tsai, medial substantia nigra and subthalamic nucleus was charted in relationship to the patterns of immunohistochemical staining in the forebrain following incubation of sections in antisera against substance P, neurotensin or leucine-enkephalin. In some cases the retrograde labeling and immunohistochemical protocols were combined in the same experiment. As a supplement, the electron microscope was utilized to investigate the ultrastructure and synaptic input of projecting cells making up populations of ventral pallidum neurons that project to different efferent targets. The results indicated that the immunocytochemical compartmentation of ventral pallidum observed in our earlier study is reflected in the organization of neurons from which ventral pallidal efferents originate. Thus, axons destined to terminate in the medial parts of substantia nigra and subthalamic nucleus project from neurons located in the lateral, neurotensin immunoreactivity-deficient part of ventral pallidum and the globus pallidus. Fibers en route to the ventral tegmental area originate in neurotensin immunoreactivity-rich medial parts of the ventral pallidum as part of a large cluster of retrogradely labeled neurons that invades several forebrain structures, including the bed nucleus of the stria terminalis, preoptic regions, and the nuclei of the diagonal band. The electron microscopic results provided additional evidence distinguishing the medial and lateral compartments of ventral pallidum. Whereas projection neurons located in both compartments display similar cytologic features, the density of synaptic input to retrogradely labeled perikarya and proximal dendrites following injections in the subthalamic nucleus is significantly greater than that seen following injections in the ventral tegmental area. Although no attempt was made to examine more distal parts of labeled dendrites in the present study, the observation that most dendritic profiles in the medial part of ventral pallidum were less contacted by boutons than their counterparts in the lateral district suggests that the level of innervation of projection neurons is generally lesser in medial ventral pallidum. This hypothesis is further supported by the presence in the medial ventral pallidum of significant numbers of "glial blockades," a cytologic configuration that is clearly capable of preventing functional interactions and is rarely observed in the lateral ventral pallidum...     

DARPP-32在大鼠全脑的定位分布

目的 探讨DARPP-32在大鼠全脑的表达分布特点.方法 应用免疫组织化学染色技术对大鼠脑内DARPP-32的表达分布进行观察.结果 免疫组织化学染色结果显示,强阳性的DARPP-32染色大部分分布于基底节区和前嗅皮质区,主要分布在伏隔核、尾壳核及杏仁核复合体的神经元胞体内,以及苍白球、腹侧苍白球、脚间核及黑质网状部的...     

Cholecystokinin innervation of the ventral striatum: a morphological and radioimmunological study

Immunocytochemistry, radioimmunological assay after surgical cuts, anterograde degeneration and retrograde tracing of fluorescent dyes were used in order to elucidate the cholecystokinin-containing afferents to the ventral striatum (nucleus accumbens, olfactory tubercle and ventral part of the caudate-putamen). In agreement with the report by Hökfelt et al.,³⁷ midbrain cholecystokinin-containing cells supply the posteromedial parts of the nucleus accumbens and olfactory tubercle, as well as the subcommissural part of caudate-putamen. Brainstem cholecystokinin afferents also reach more rostral parts of the ventral striatum including the rostrolateral olfactory tubercle. The ascending cholecystokinin axons enter the medial forebrain bundle at the meso-diencephalic border and maintain a rough medial to lateral topography at the caudal diencephalon. A second major cholecystokinin pathway, with possible origin in the piriform and medial prefrontal cortices and/or the amygdala, projects to the subcommissural caudate-putamen, the olfactory tubercle, the lateral part of the nucleus accumbens and the dorsal part of the bed nucleus of stria terminalis. Finally, the rostral part of the dorsal caudate-putamen receives a substantial cholecystokinin innervation from the basolateral amygdala and possibly from the neocortex. According to radioimmunological data, the descending telencephalic cholecystokinin system accounts for about 60% of all cholecystokinin in the rostral forebrain.The combined use of morphological and biochemical methods provided evidence for a partially overlapping distribution and possible interaction between an ascending brainstem and descending telencephalic cholecystokinin fiber systems within the striatum and related rostral forebrain areas.     

Ventral striatal anatomy of locomotor activity induced by cocaine,D-amphetamine,dopamine and D1/D2 agonists

The ventral striatum appears to play a critical role in mediating motoric effects (i.e. ambulatory activity and rearing) of psychostimulants such as cocaine. We evaluated whether sub-regions of the ventral striatum play differential roles in locomotion and rearing induced by various dopaminergic drugs. Injections of D-amphetamine and dopamine stimulated locomotion and rearing with a similar potency at each of the sub-regions: the core, medial shell or medial tubercle. However, injections of mixtures of the D(1)- and D(2)-type agonists SKF 38393 and quinpirole or cocaine into the medial olfactory tubercle or the medial shell of the nucleus accumbens induced marked locomotion and rearing, while these injections into the core induced little or no locomotion or rearing. Furthermore, cocaine injections into the lateral or posterior tubercle produced marginal locomotion and rearing, while cocaine injections into regions just dorsal to these tubercle sites, the lateral portion of the shell or the ventral pallidum, did not produce any stimulating effect. We conclude that dopaminergic compounds induce vigorous locomotion and rearing in both core and shell; the relative roles of the core and shell differ depending on chemical compounds. Similar to the nucleus accumbens, the olfactory tubercle, particularly the medial portion, also mediates these behaviors induced by dopaminergic compounds. The medial ventral striatum (i.e. the medial tubercle and medial shell) plays a more important role in cocaine-induced locomotion and rearing than the lateral ventral striatum (i.e. the core, lateral shell and lateral tubercle). Moreover, the differential effects of cocaine between the medial and lateral portions of the shell on locomotion and rearing suggest more than two functional units (the core vs. the shell) within the accumbens.     

The globus pallidus and its rostroventral extension into the olfactory tubercle of the rat: A cyto- and chemoarchitectural study

The globus pallidus is characterized by a high iron content and the distribution of the ferric iron in the rat brain provides evidence that globus pallidus extends rostroventrally below the anterior commissure and into the olfactory tubercle. The extension of the globus pallidus into the olfactory tubercle is consistent with the notion of the ventral striatum.¹⁴ in the sense that it provides for an expected close proximity between the striatum and the globus pallidus throughout the dorsoventral extent of the corpus striatum. The distribution of enkephalin. and of acetylcholinesterase- and succinate dehydrogenase-positive neurons is also consistent with an extension of the ventral part of globus pallidus to the base of the forebrain in the rat.Since part of the ventral pallidum corresponds to a region that is usually referred to as the subcommissural part of the substantia innominata, it seems reasonable to restrict the term substantia innominata to the more caudally-located sublenticular part of the substantia innominata.     

Distribution of the high-affinity choline transporter in the central nervous system of the rat

In cholinergic nerve terminals, Na(+)- and Cl(-)-dependent, hemicholinium-3-sensitive, high-affinity choline uptake is thought to be the rate-limiting step in acetylcholine synthesis. The high-affinity choline transporter cDNA responsible for the activity was recently cloned. Here we report production of a highly specific antibody to the high-affinity choline transporter and distribution of the protein in the CNS of the rat. The antibody stained almost all known cholinergic neurons and their terminal fields. High-affinity choline transporter-immunoreactive cell bodies were demonstrated in the olfactory tubercle, basal forebrain complex, striatum, mesopontine complex, medial habenula, cranial nerve motor nuclei, and ventral horn and intermediate zone of the spinal cord. Noticeably, high densities of high-affinity choline transporter-positive axonal fibers and puncta were encountered in many brain regions such as cerebral cortex, hippocampus, amygdala, striatum, several thalamic nuclei, and brainstem. Transection of the hypoglossal nerve resulted in a loss of high-affinity choline transporter immunoreactivity in neurons within the ipsilateral hypoglossal motor nucleus, which paralleled a loss of immunoreactivity to choline acetyltransferase. The antibody also stained brain sections from human and mouse, suggesting cross-reactivity.These results confirm that the high-affinity choline transporter is uniquely expressed in cholinergic neurons and is efficiently transported to axon terminals. The antibody will be useful to investigate possible changes in cholinergic cell bodies and axon terminals in human and rodents under various pathological conditions.     

Immunohistochemical localization of DARPP-32 in the brain and spinal cord of anuran amphibians and its relation with the catecholaminergic system

The relationship between dopaminergic neuronal structures and dopaminoceptive structures in the amphibian brain and spinal cord are assessed by means of single and double immunohistochemical techniques with antibodies directed against DARPP-32 (a phosphoprotein related to the dopamine D(1)-receptor) and tyrosine hydroxylase (TH) applied to the brain of the anurans Rana perezi and Xenopus laevis. The DARPP-32 antibody yielded a well-differentiated pattern of staining in the brain of these anurans. In general, areas that are densely innervated by TH-immunoreactive fibers such as the nucleus accumbens, striatum, amygdaloid complex, thalamus, optic tectum, torus semicircularis and spinal cord display a remarkable immunoreactivity for DARPP-32 in cell bodies and neuropil. Distinct cellular DARPP-32 immunoreactivity was also found in the septum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, habenula, retina, midbrain tegmentum, rhombencephalic reticular formation and solitary tract nucleus. Hodological data supported that striatal projection neurons were DARPP-32 immunoreactive. Double immunohistofluorescence staining revealed that catecholaminergic cells generally do not stain for DARPP-32, except for some cells in the ventral mesencephalic tegmentum of Xenopus and cells in the nucleus of the solitary tract of Rana. Several interspecies differences were noted for the DARPP-32 distribution in the brain of the two anurans, namely in the habenula, the thalamus and prethalamus, the cerebellum and octavolateral area and the structures with DARPP-32/TH colocalization. However, in general, the distribution of DARPP-32 in the brain of the anuran amphibians resembles in many aspects the pattern observed in amniotes, especially in reptiles.     

Efferent connections of the rostral linear nucleus of the ventral tegmental area in the rat

The ventral tegmental area (VTA) is crucially involved in brain reward, motivated behaviors, and drug addiction. This district is functionally heterogeneous, and studying the connections of its different parts may contribute to clarify the structural basis of intra-VTA functional specializations. Here, the efferents of the rostral linear nucleus (RLi), a midline VTA component, were traced in rats with the Phaseolus vulgaris leucoagglutinin (PHA-L) technique. The results show that the RLi heavily innervates the olfactory tubercle (mainly the polymorph layer) and the ventrolateral part of the ventral pallidum, but largely avoids the accumbens. The RLi also sends substantial projections to the magnocellular preoptic nucleus, lateral hypothalamus, central division of the mediodorsal thalamic nucleus, lateral part of the lateral habenula and supraoculomotor region, and light projections to the prefrontal cortex, basolateral amygdala, and dorsal raphe nucleus. A similar set of projections was observed after injections in rostromedial VTA districts adjacent to RLi, but these districts also send major outputs to the lateral ventral striatum. Overall, the data suggest that the RLi is a distinct VTA component in that it projects primarily to pallidal regions of the olfactory tubercle and to their diencephalic targets, the central division of the mediodorsal thalamic nucleus and the lateral part of the lateral habenula. Because the rat RLi reportedly contains a lower density of dopaminergic neurons as compared with most of the VTA, its unusual projections may reflect a non-dopaminergic, putative GABAergic, phenotype, and this distinctive cell population seemingly extends beyond RLi boundaries into the laterally adjacent VTA. By being connected to the central division of the mediodorsal thalamic nucleus (directly and via ventral striatopallidal system) and to the magnocellular preoptic nucleus, the RLi and its surroundings may play a role in olfactory-guided behaviors, which are part of the approach responses associated with appetitive motivational states.     

Excitatory amino acid binding sites in the basal ganglia of the rat: a quantitative autoradiographic study.

Quantitative receptor autoradiography was used to determine the distribution of excitatory amino acid binding sites in the basal ganglia of rat brain. alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-D-aspartate, kainate, quisqualate-sensitive metabotropic and non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had their highest density in striatum, nucleus accumbens, and olfactory tubercle. Kainate binding was higher in the lateral striatum but there was no medial-lateral striatal gradient for other binding sites. N-Methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding sites were most dense in the nucleus accumbens and olfactory tubercle. There was no dorsal-ventral gradient within the striatal complex for the other binding sites. Other regions of the basal ganglia had lower densities of ligand binding. To compare binding site density within non-striatal regions, binding for each ligand was normalized to the striatal binding density. When compared to the striatal complex, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and metabotropic binding sites had higher relative density in the globus pallidus, ventral pallidum, and subthalamic nucleus than other binding sites. Metabotropic binding also had a high relative density in the substantia nigra. Non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had a high relative density in globus pallidus, ventral pallidum, and substantia nigra. N-Methyl-D-aspartate binding sites had a low relative density in pallidum, subthalamic nucleus, substantia nigra and ventral tegmental area. Our data indicate heterogeneous distribution of excitatory amino acid binding sites within rat basal ganglia and suggest that the character of excitatory amino acid-mediated neurotransmission within the basal ganglia is also heterogeneous.     

Neurocircuitries of the basal ganglia studied in organotypic cultures: focus on tyrosine hydroxylase, nitric oxide synthase and neuropeptide immunocytochemistry

The nigrostriatal and mesolimbic systems of the rat were reconstructed using an organotypic culture model, whereby neonatal brain tissue was grown in vitro for approximately one month. The nigrostriatal system comprised of tissue from the substantia nigra, the dorsal striatum and the frontoparietal cortex, while the mesolimbic system included the ventral tegmental area, ventral striatum (including the fundus striati, accumbens nucleus, olfactory tubercle, lateral septum, ventral pallidum and piriform cortex) and cingulate cortex. These regions were also cultured alone or in pairs. The cultures were monitored in vitro, and after one month fixed in a formalin-picric acid solution, and processed for immunohistochemistry using antibodies raised against tyrosine hydroxylase, nitric oxide synthase, preprocholecystokinin, glutamate decarboxylase, neuropeptide Y, dopamine- and cyclic AMP-regulated phosphoprotein-32 and glial fibrillary acidic protein. The tissue survived in single, double or triple cultures, although differences were found depending upon the source and combination of cultured region. Neurons had localization and shape as in vivo. Local networks were especially prominent in the mesencephalon, where both tyrosine hydroxylase-positive axons spread from the "substantia nigra" to the rest of the tissue, and where nitric oxide synthase-positive networks also surrounded tyrosine hydroxylase-positive neurons. Glutamate decarboxylase-positive nerve terminals formed dense networks around tyrosine hydroxylase-positive neurons. In the striatum, nitric oxide synthase and dopamine- and cyclic AMP-regulated phosphoprotein-32 neurons were surrounded by tyrosine hydroxylase-positive nerve terminals. The nigral and ventral tegmental area dopamine neurons projected to striatal and cortical structures, but the projection from the ventral tegmental area to the cingulate cortex was more prominent. With regard to co-existence, preprochole-cystokinin-like immunoreactivities was found in many tyrosine hydroxylase-positive neurons and neuropeptide Y- and nitric oxide synthase-like immunoreactivity co-existed in striatal and cortical tissues. In general terms, the chemical neuroanatomy in the cultures was similar to that described earlier in vivo. Nitric oxide synthase staining was particularly intense. Taken together, the organotypic model captures many of the morphological and neurochemical features seen in vivo, providing a valuable model for studying neurocircuitries of the brain in detail, where 'normal' and 'pathological' conditions can be simulated.