Differential loss of striatal projection systems in Huntington's disease: a quantitative immunohistochemical study

Prior studies suggest differences exist among striatal projection neuron types in their vulnerability to Huntington's disease (HD). In the present study, we immunolabeled the fibers and terminals of the four main types of striatal projection neuron in their target areas for substance P, enkephalin, or glutamic acid decarboxylase (GAD), and used computer-assisted image analysis to quantify the abundance of immunolabeled terminals in a large sample of HD cases ranging from grade 0 to grade 4 [J. Neuropathol. Exp. Neurol. 44 (1985) 559], normalized to labeling in control human brains. Our goal was to characterize the relative rates of loss of the two striatopallidal projection systems (to the internal versus the external pallidal segments) and the two striatonigral projections systems (to pars compacta versus pars reticulata). The findings for GAD and the two neuropeptides were similar--the striatal projection to the external pallidal segment was the most vulnerable, showing substantial loss by grade 1. Loss of fibers in both subdivisions of the substantia nigra was also already great by grade 1. By contrast, the loss in the striatal projection system to the internal segment of globus pallidus proceeded more gradually. By grade 4 of HD, however, profound loss in all projection systems was apparent. These findings support the notion that the striatal neurons preferentially projecting to the internal pallidal segment are, in fact, less vulnerable in HD than are the other striatal projection neuron types.     

Localization of cannabinoid receptor in the human developing and adult basal ganglia. Higher levels in the striatonigral neurons.

In the infant and adult human basal ganglia, the finding of mRNA exclusively in the striatal medium-sized neurons together with the detection of [3H]CP55,940 binding sites in the caudate-putamen, accumbens, substantia nigra pars reticulata and globus pallidus suggests cannabinoid receptor localization on the striatal intrinsic enkephalinergic and substance P-projecting neurons and on their nigral and pallidal terminals. However, the consistent finding of higher binding in the substantia nigra pars reticulata and medial part of the globus pallidus over its lateral segment suggests cannabinoid receptor enrichment on the striatal substance P neurons which express selectively the dopamine D1 receptor.     

The postsynaptic targets of substance P-immunoreactive terminals in the rat neostriatum with particular reference to identified spiny striatonigral neurons

Summary Substance P-immunoreactive boutons were examined in the electron microscope in sections of the rat neostriatum that contained retrogradely labelled striatonigral neurons and/or Golgi-impregnated medium-size densely spiny neurons. The postsynaptic targets of the immunoreactive boutons were characterized on the basis of ultrastructural features, their projection to the substantia nigra and/or their somato-dendritic morphology. Substance P-immunoreactive axonal boutons formed symmetrical synaptic specializations. Of a total of 233 randomly identified synaptic boutons 72.5% made contact with dendritic shafts, 15% with dendritic spines and 10.7% with perikarya. The ultrastructural characteristics of some of the postsynaptic neuronal perikarya were consistent with their identification as striatal interneurons. Similarly, the observation of some of the substance P-containing terminals in contact with spines, spine-bearing dendritic shafts and perikarya with the ultrastructural characteristics of medium-size densely spiny neurons suggested that one of the targets of substance P-positive terminals are striatal projection neurons. Direct evidence for this was obtained in sections from rats that had received injections of horseradish peroxidase conjugated with wheatgerm agglutinin in the substantia nigra. The perikarya of retrogradely labeled striatonigral neurons were found to receive symmetrical synaptic input from substance P-positive boutons. Ultrastructural analysis of Golgi-impregnated medium-size densely spiny neurons, some of which were also retrogradely labeled from the substantia nigra, demonstrated directly that this class of neuron was postsynaptic to the substance P-immunoreactive boutons. The combination of Golgi-impregnation with substance P-immunocytochemistry made it possible to study the pattern or topography of the substance P-positive input to medium size densely spiny neurons. The substance P-containing boutons made contact predominantly with perikarya and dendritic shafts. This pattern of input is markedly different from that of other identified inputs to medium-size densely spiny neurons.     

Correlation between met-enkephalin and substance P immunoreactivity in the primate globus pallidus

Using immunohistochemical techniques, the distribution of enkephalin and substance P immunoreactive fibers and terminals was studied in the globus pallidus of the non-human primate. In the external segment of the globus pallidus, enkephalin immunoreactivity was very dense while only sparse to moderate substance P staining was observed. Enkephalin immunoreactivity in the inner portion of the internal segment was moderate while such fibers were sparse in the outer portion of the internal segment. Substance P immunoreactivity was dense throughout the internal segment of the globus pallidus.The pattern of enkephalin and substance P immunoreactivity in the globus pallidus of the non-human primate as reported in the present study is of interest with regard to pallidal efferents. The pallidosubthalmic projection, arising from the external segment of the globus pallidus, is likely to be strongly influenced by the very dense network of enkephalin immunoreactive fibers and terminals in this region. Conversely, substance P immunoreactive elements are sparse in the external segment, and are, therefore, unlikely to influence significantly activity carried by the pallidosubthalmic projection. Since the inner portion of the internal segment contains moderate enkephalin immunoreactivity and dense substance P immunoreactivity, the information carried by the lenticular fasiculus may be modulated by both of these putative transmitters. On the other hand, based on the densities of immunoreactivity, the ansa lenticularis, which arises from the outer portion of the internal segment, is likely to be under greater influence of the dense substance P projection to this area.     

Immunohistochemical localization of DARPP32 in striatal projection neurons and striatal interneurons in pigeons

DARPP32 is a D1-receptor associated signaling protein found in striatal projection neurons in mammals, including both substance P-containing (SP+) neurons and enkephalinergic (ENK+) projection neurons. The present study used immunohistochemical single- and double-labeling to examine the cellular localization of DARPP32 in pigeon striatum. Single-label studies revealed that DARPP32 is present in numerous medium-sized striatal perikarya and DARPP32+ axons and terminals were seen to profusely innervate the two major striatal projection targets, the pallidum and the substantia nigra. The single-labeling studies indicated that about 60% of all striatal perikarya labeled for DARPP32+ in striatum, which exceeds the abundance of either SP+ or ENK+ perikarya. Single-labeling studies also showed that the abundance of DARPP32+ fibers and terminals in pallidum exceeds that of either SP+ or ENK+ fibers and terminals in pallidum. Double-labeling found that 30–50% of striatal SP+ perikarya and 7–24% of ENK+ striatal perikarya labeled for DARPP32 in pigeon, and confirmed that DARPP32 was found in both SP+ and ENK+ fibers and terminals in pallidum. In contrast to its prevalence in striatal projection neurons, DARPP32 was virtually absent from cholinergic and NPY+ striatal interneurons, as also true in mammals. Our data are consistent with the interpretation that many SP+ neurons and many ENK+ neurons in avian striatum possess D1-type dopamine receptors and use a DARPP32 signalling pathway, although this may be more common for SP+ than for ENK+ neurons.     

The distribution of enkephalin immunoreactive fibers and terminals in the monkey central nervous system: An immunohistochemical study

Using immunohistochemical techniques, the distribution of met-enkephalin fibers and terminals was studied in the central nervous system of adult old-world monkeys. Areas which showed the greatest density of immunoreactivity included substantia gelatinosa, nucleus tractus solitarius, nucleus parabrachialis, substantia nigra, median eminence, globus pallidus (external segment), patches within the striatum and the region of nucleus accumbens and the olfactory area. Striking and discrete zones of enkephalin immunoreactive fibers and terminals which did not conform to known nuclear boundaries were observed in the latter areas.The distribution of enkephalin in the monkey is compared to what has been described in the rat central nervous system. In general, the two species are similar, however, differences were observed in some areas including the hypoglossal nucleus, substantia nigra and in the region of the nucleus accumbens and olfactory area. The results are discussed with regard to the possible functional significance of enkephalin localization in regions related to regulation of pain, mood, and autonomie function.     

Efferent fibers of the subthalamic nucleus in the monkey. A comparison of the efferent projections of the subthalamic nucleus,substantia nigra and globus pallidus

A study was made to determine the efferent projections of the subthalamic nucleus in the monkey. Because of the impossibility of producing lesions in this nucleus, not involving adjacent structures, lesions were produced by different stereotaxic approaches. Comparisons were made with degeneration resulting from localized lesions in substantia nigra and globus pallidus. Degeneration resulting from these lesions was studied in transverse and sagittal sections stained by the Nauta-Gygax method. Efferent fibers from the subthalamic nucleus pass through the internal capsule into the medial pallidal segment; a few fibers are distributed to the lateral pallidum. Some subthalamic efferent fibers pass to the contralateral globus pallidus via the dorsal supraoptic decussation, but none projection to the thalamus. Nigral efferent fibers project to parts of the ventral anterior (VAmc) and ventral lateral (VLm) thalamic nuclei. The medial pallidal segment gives fibers to: (1) ventral anterior (VA), ventral lateral (VLo) and centromedian (CM) thalamic nuclei, and (2) the pedunculopontine nucleus. The lateral pallidal segment projects exclusively to the subthalamic nucleus. Thalamic projections of the substania nigra and globus pallidus are distinctive. Subthalamic projections to the globus pallidus are more profuse than those of the substantia nigra. The following hypothesis is presented: Subthalamic dyskinesia, due to lesions in the subthalamic nucleus, is a consequence of removal of inhibitory influences acting upon the medial segment of the globus pallidus.     

Synaptic organization of GABAergic inputs from the striatum and the globus pallidus onto neurons in the substantia nigra and retrorubral field which project to the medullary reticular formation.

Anatomical tract-tracing and immunohistochemical techniques involving correlated light and electron microscopy were used to determine whether the descending striatal and pallidal afferents to the substantia nigra pars reticulata converge onto individual neurons projecting to the pontomedullary and medullary reticular formation in the rat. Injections of biocytin into the ventrolateral region of the striatum and Phaseolus vulgaris-leucoagglutinin into the ventrolateral and caudal regions of the globus pallidus led to overlapping anterogradely labelled terminal fields within the dorsolateral substantia nigra pars reticulata. These terminal fields were punctuated by neurons which had been retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into the lateral pontomedullary reticular formation. The anterogradely labelled striatal and pallidal terminals displayed different morphological characteristics; the striatal terminals were small and diffusely distributed throughout the neuropil without any particular neuronal association whereas the pallidal terminals were large and formed pericellular baskets around the perikarya of retrogradely and non-retrogradely labelled nigral neurons. In areas of the substantia nigra where there was an overlap between the two terminal fields, individual retrogradely labelled nigroreticular neurons were found to be apposed by both sets of anterogradely labelled terminals. Electron microscopic analysis revealed that the striatonigral and pallidonigral terminals displayed different ultrastructural features, the striatal terminals were small, contained few mitochondria and formed symmetric synaptic contacts predominantly with the distal dendrites of nigroreticular neurons whereas the pallidal terminals were large, contained numerous mitochondria and formed symmetric synaptic contacts preferentially with perikarya and proximal dendrites of nigroreticular neurons. Post-embedding immunohistochemical staining revealed that both striatonigral and pallidonigral terminals, some which formed synaptic contact with nigroreticular neurons, displayed GABA immunoreactivity. Examination of twelve retrogradely labelled neurons in the electron microscope revealed that all received synaptic inputs from both sets of anterogradely labelled terminals. In addition to the substantia nigra pars reticulata, neurons of the retrorubral field were also retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into pontomedullary reticular formation. These retrorubroreticular neurons were part of a continuum of labelled cells which extended from the dorsolateral substantia nigra pars reticulata caudally into the retrorubral field. When combined with anterograde tracing methods it was found that the retrorubroreticular neurons received synaptic inputs from pallidal terminals which were morphologically similar to the pallidonigral terminals and formed symmetric synapses with the neuronal somata and proximal dendrites. In contrast to nigroreticular neurons, the stratonigral terminals were not seen in contact with retrorubroreticular cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dopamine-opiate interaction in the regulation of neostriatal and pallidal neuronal activity as assessed by opioid precursor peptides and glutamate decarboxylase messenger RNA expression.

Neostriatal GABAergic neurons projecting to the globus pallidus synthesize the opioid peptide enkephalin, while those innervating the substantia nigra pars reticulata and the entopeduncular nucleus synthesize dynorphin. The differential control exerted by dopamine on the activity of these two efferent projections concerns also the biosynthesis of these opioid peptides. Using in situ hybridization histochemistry, we investigated the role of opioid co-transmission in the regulation of neostriatal and pallidal activity. The expression of the messenger RNAs encoding glutamate decarboxylase-the biosynthetic enzyme of GABA-and the precursor peptides of enkephalin (preproenkephalin) and dynorphin (preprodynorphin) were measured in rats after a sustained blockade of opioid receptors by naloxone (s.c. implanted osmotic minipump, eight days, 3 mg/kg per h), and/or a subchronic blockade of D2 dopamine receptors by haloperidol (one week, 1.25 mg/kg s.c. twice a day). The density of mu opioid receptors in the neostriatum and globus pallidus was determined by autoradiography. Naloxone treatment resulted in a strong up-regulation of neostriatal and pallidal mu opioid receptors that was not affected by the concurrent administration of haloperidol. Haloperidol alone produced a moderate down-regulation of neostriatal and pallidal micro opioid receptors. Haloperidol strongly stimulated the expression of neostriatal preproenkephalin and preprodynorphin messenger RNAs. This effect was partially attenuated by naloxone, which alone produced moderate increases in preproenkephalin and preprodynorphin messenger RNA levels. In the neostriatum, naloxone did not affect either basal or haloperidol-stimulated glutamate decarboxylase messenger RNA expression. A strong reduction of glutamate decarboxylase messenger RNA expression was detected over pallidal neurons following either naloxone or haloperidol treatment, but concurrent administration of the two antagonists did not result in a further decrease. The amplitude of the variations of mu opioid receptor density and of preproenkephalin and preprodynorphin messenger RNA levels suggests that the regulation of neostriatal and pallidal micro opioid receptors is more susceptible to a direct opioid antagonism, while the biosynthesis of opioid peptides in the neostriatum is more dependent on the dopaminergic transmission. The down-regulation of mu opioid receptors following haloperidol represents probably an adaptive change to increased enkephalin biosynthesis and release. The haloperidol-induced increase in neostriatal preprodynorphin messenger RNA expression might result from an indirect, intermittent stimulation of neostriatal D1 receptors. The haloperidol-induced decrease of pallidal glutamate decarboxylase messenger RNA expression suggests, in keeping with the current functional model of the basal ganglia, that the activation of the striatopallidal projection produced by the interruption of neostriatal dopaminergic transmission reduces the GABAergic output of the globus pallidus. The reduction of pallidal glutamate decarboxylase messenger RNA expression following opioid receptor blockade indicates an indirect, excitatory influence of enkephalin upon globus pallidus neurons and, consequently, a functional antagonism between the two neuroactive substances (GABA and enkephalin) of the striatopallidal projection in the control of globus pallidus output. Through this antagonism enkephalin could partly attenuate the GABA-mediated effects of a dopaminergic denervation on pallidal neuronal activity.     

Single-cell RT-PCR, in situ hybridization histochemical, and immunohistochemical studies of substance P and enkephalin co-occurrence in striatal projection neurons in rats

Single-cell RT-PCR studies in 3-4-week-old rats have raised the possibility that as many as 20% of striatal projection neurons may be a unique type that contains both substance P (SP) and enkephalin (ENK). We used single-cell RT-PCR, retrograde labeling, in situ hybridization histochemistry, and immunolabeling to characterize the abundance of this cell type, its projection target(s), and any developmental changes in its frequency. We found by RT-PCR that 11% of neurons containing either SP or ENK contained both in 4-week-old rats, while in 4-month-old rats SP/ENK colocalization was only 3%. SP-only neurons tended to co-contain dynorphin and ENK-only neurons neurotensin, while SP/ENK neurons tended to contain dynorphin. Single-cell RT-PCR showed SP/ENK co-occurrence in 4-week-old rats to be no more common among striatal neurons retrogradely labeled from the substantia nigra than among those retrogradely labeled from globus pallidus. Double-label in situ hybridization showed SP/ENK perikarya to be scattered throughout striatum, making up 8% of neurons containing either SP or ENK at 4 weeks, but only 4% at 4 months. Immunolabeling showed that presumptive striatal terminals in globus pallidus externus, globus pallidus internus and substantia nigra pars reticulata that colocalized SP and ENK were scarce. Terminals colocalizing SP and ENK were, however, abundant in the substantia nigra pars compacta. Thus, SP-only and ENK-only neurons make up the vast majority of striatal projection neurons in rats, the frequency of SP/ENK colocalizing striatal neurons is low in adult rats (3-4%), and SP/ENK colocalizing neurons primarily project to SNc but do not appear to be confined to striosomes.     

A horseradish peroxidase study of afferent connections of the globus pallidus in Macaca mulatta

Summary The high tonic discharge rates of globus pallidus neurons in awake monkeys suggest that these neurons may receive some potent excitatory input. Because most current electrophysiological evidence suggests that the major described pallidal afferent systems from the neostriatum are primarily inhibitory, we used retrograde transport of horseradish peroxidase (HRP) to identify possible additional sources of pallidal afferent fibers. The appropriate location was determined before HRP injection by mapping the characteristic high frequency discharge of single pallidal units in awake animals. In animals with injections confined to the internal pallidal segment, retrograde label was seen in neurons of the pedunculopontine nucleus, dorsal raphe nucleus, substantia nigra, caudate, putamen, subthalamic nucleus, parafascicular nucleus, zona incerta, medial and lateral subthalamic tegmentum, parabrachial nuclei, and locus coeruleus. An injection involving the external pallidal segment and the putamen as well resulted in additional labeling of cells in centromedian nucleus, pulvinar, and the ventromedial thalamus.Abbreviations AC anterior commissure - CG central grey - CM centromedian nucleus - CN caudate nucleus - DM dorsomedial nucleus - DR dorsal raphe nucleus - DSCP decussation of superior cerebellar peduncle - GPe globus pallidus, external segment - GPi globus pallidus, internal segment - LC locus coeruleus - LL lateral lemniscus - MG medial geniculate nucleus - ML medial lemniscus - NVI abducens nucleus - OT optic tract - Pbl lateral parabrachial nucleus - Pbm medial parabrachial nucleus - Pf parafascicular nucleus - PPN pedunculopontine nucleus - PuO oral pulvinar nucleus - RN red nucleus - SCP superior cerebellar peduncle - SI substantia innominata - SNc substantia nigra, pars compacta - SNr substantia nigra, pars reticulata - STN subthalamic nucleus - TMT mamillothalamic tract - VA ventral anterior nucleus - VLc ventral lateral nucleus, pars caudalis - VLm ventral lateral nucleus, pars medialis - VLo ventral lateral nucleus, pars oralis - VPI ventral posterior inferior nucleus - VPM ventral posterior medial nucleus - VPLc ventral posterior lateral nucleus, pars caudalis - ZI zona incerta     

Activation of nigral and pallidal dopamine D1-like receptors modulates basal ganglia outflow in monkeys

Studies of the effects of dopamine in the basal ganglia have focused on the striatum, whereas the functions of dopamine released in the internal pallidal segment (GPi) or in the substantia nigra pars reticulata (SNr) have received less attention. Anatomic and biochemical investigations have demonstrated the presence of dopamine D1-like receptors (D1LRs) in GPi and SNr, which are primarily located on axons and axon terminals of the GABAergic striatopallidal and striatonigral afferents. Our experiments assessed the effects of D1LR ligands in GPi and SNr on local gamma-aminobutyric acid (GABA) levels and neuronal activity in these nuclei in rhesus monkeys. Microinjections of the D1LR receptor agonist SKF82958 into GPi and SNr significantly reduced discharge rates in GPi and SNr, whereas injections of the D1LR antagonist SCH23390 increased firing in the majority of GPi neurons. D1LR activation also increased bursting and oscillations in neuronal discharge in the 3- to 15-Hz band in both structures, whereas D1LR blockade had the opposite effects in GPi. Microdialysis measurements of GABA concentrations in GPi and SNr showed that the D1LR agonist increased the level of the transmitter. Both findings are compatible with the hypothesis that D1LR activation leads to GABA release from striatopallidal or striatonigral afferents, which may secondarily reduce firing of basal ganglia output neurons. The antagonist experiments suggest that a dopaminergic "tone" exists in GPi. Our results support the finding that D1LR activation may have powerful effects on GPi and SNr neurons and may mediate some of the effects of dopamine replacement therapies in Parkinson's disease.     

The relationship between ventral striatal efferent fibers and the distribution of peptide-positive woolly fibers in the forebrain of the rhesus monkey.

Peptidergic fibers in the globus pallidus of the monkey appear in the morphological form referred to as woolly fibers. These fibers are composed of a dense plexus of thin beaded axons which ensheath an unstained central core. Such structures are not confined to the globus pallidus, but are also present in the bed nucleus of the stria terminalis, the hypothalamus, the dorsal part of the amygdala, and ventrally in the basal forebrain. The present study describes the relationship between projections from the rostral and ventral striatum and the enkephalin- and substance P-positive woolly fibers. Following injections of either tritiated amino acids or the lectin Phaseolus vulgaris-leucoagglutinin in the ventral striatum, anterogradely labeled fibers and terminals in the forebrain were visualized simultaneously with enkephalin- or substance P immunoreactivity in the same tissue section in order to determine: (i) the extent to which the woolly fiber distribution represents striatal output systems; (ii) whether woolly fibers can be considered as a marker for the entire striatal forebrain projection; and (iii) whether enkephalin and substance P are involved differentially in distinct ventral striatopallidal pathways. Phaseolus vulgaris-leucoagglutinin labeling is seen in the globus pallidus and adjacent structures either as single, beaded fibers or in a profile strikingly similar to that of woolly fibers. In tissue sections treated for a double immunohistochemical protocol, following which the Phaseolus vulgaris-leucoagglutinin-immunoreactive fibers turn black and the peptidergic woolly fibers brown; many of the lectin-positive fibers are seen to enter the peptide-positive woolly fiber plexus. Likewise, following the injections with tritiated amino acids in the ventral striatum, coarse structures that have dimensions resembling those of the woolly fibers are identified. In sections immunohistochemically stained and subsequently treated for autoradiography, peptide-positive woolly fibers can be identified underlying the silver grains. In sections stained for both peptide immunoreactivity and tracer substances, enkephalin or substance P-positive woolly fibers are present in all pallidal regions that receive ventral striatal input. However, the ventral striatum also sends fibers to the hypothalamus, bed nucleus of the stria terminalis, the dorsal part of the amygdala, the septum, the preoptic area, and other areas of the basal forebrain. In these nuclei the peptide-positive woolly fiber distribution is less extensive than the terminal labeling. The distribution of substance P-positive fibers in the subcommissural pallidal region is more limited than the distribution of enkephalinergic fibers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Enkephalin regulates acute D2 dopamine receptor antagonist-induced immediate-early gene expression in striatal neurons.

Projection neurons of the striatum release opioid peptides in addition to GABA. Our previous studies showed that the opioid peptide dynorphin regulates that subtype of projection neurons which sends axons to the substantia nigra/entopeduncular nucleus, as indicated by an inhibitory action of dynorphin/agonists on D1 dopamine receptor-mediated immediate-early gene induction in these neurons. The other subtype of striatal projection neurons projects to the globus pallidus and contains the opioid peptide enkephalin. Here, we investigated whether enkephalin regulates the function of striatopallidal neurons, by analysing opioid effects on immediate-early gene induction by D2 dopamine receptor blockade that occurs in these neurons. Thus, the effects of systemic and intrastriatal administration of various opioid receptor agonists and antagonists on immediate-early gene expression (c-fos, zif 268) induced by the D2 receptor antagonist eticlopride were examined with in situ hybridization histochemistry. Intrastriatal infusion of enkephalin (delta and mu), but not dynorphin (kappa), receptor agonists suppressed immediate-early gene induction by eticlopride in a dose-dependent manner. This suppression was blocked by the opioid receptor antagonist naloxone, confirming the involvement of opioid receptors. Repeated treatment with D2 receptor antagonists produces increased enkephalin expression and diminished immediate-early gene inducibility in striatopallidal neurons, as well as behavioral effects that are attenuated compared to those of acute treatment (e.g., reduced akinesia). Naloxone reversed such behavioral recovery (i.e. reinstated akinesia), but did not significantly affect suppressed immediate-early gene induction. Our results indicate that enkephalin acts, via mu and delta receptors in the striatum, to inhibit acute effects of D2 receptor blockade in striatopallidal neurons. Moreover, the present findings suggest that increased enkephalin expression after repeated D2 receptor antagonist treatment is an adaptive response that counteracts functional consequences of D2 receptor blockade, but is not involved in suppressed immediate-early gene induction. Together with our earlier findings of the role of dynorphin, these results indicate that opioid peptides in the striatum serve as negative feedback systems to regulate the striatal output pathways in which they are expressed.     

D1 and D2 dopamine receptors differentially regulate c-fos expression in striatonigral and striatopallidal neurons.

The expression of Fos, the product of the proto-oncogene c-fos, is thought to be a marker of neuronal activity. D1, but not D2, dopamine receptor agonists have previously been shown to increase Fos immunoreactivity in striatonigral neurons ipsilateral to a 6-hydroxydopamine lesion of the nigrostriatal pathway. In the present study, it was demonstrated that the D1 receptor agonist SKF 38393 rarely increased Fos in striatopallidal neurons of the 6-hydroxydopamine denervated striatum. Conversely, in the intact striatum, the D2 receptor antagonist haloperidol enhanced Fos expression predominantly in striatopallidal neurons labelled retrogradely from the globus pallidus or with an oligonucleotide probe complementary to mRNA encoding enkephalin. These results are consistent with studies suggesting that D1 receptors are located predominantly on striatonigral neurons and that D2 receptors reside principally on enkephalin-containing striatopallidal neurons. They also provide a neuroanatomical basis for neurochemical and neurophysiological observations indicating that dopamine facilitates the activity of striatonigral neurons but inhibits striatopallidal neurons. In another experiment the selective D2 receptor agonist quinpirole was found to increase Fos immunoreactivity in the globus pallidus ipsilateral to a 6-hydroxydopamine lesion. It is proposed that this may have been due to a D2 receptor-mediated inhibition of enkephalin and GABA release from striatopallidal terminals that in turn disinhibited the pallidal neurons. In a final series of experiments, brain microdialysis was used to determine the location of dopamine receptors regulating striatal Fos expression. Local application of the selective D1 receptor agonist CY 208-243 in the 6-hydroxydopamine-denervated striatum, or of haloperidol in the intact striatum via the dialysis probe increased Fos immunoreactivity in the immediate vicinity of the probe. Hence, the inductive effects of these systematically administered compounds on Fos expression in the striatum are mediated at least partly by local dopamine receptors in the striatum. Taken together, these results suggest that the differential regulation of striatonigral and striatopallidal activity by dopamine is mediated by the largely separate location of D1 and D2 receptors on these outputs.     

Convergence of synaptic inputs from the striatum and the globus pallidus onto identified nigrocollicular cells in the rat: a double anterograde labelling study.

Two major sources of afferent synaptic inputs to projection neurons in the rat substantia nigra reticulata are the striatum and the globus pallidus. In order to understand better the functional relationships between these two afferents in the control of the activity of nigrofugal neurons, experiments have been performed to test the possibility that single nigrofugal cells receive convergent synaptic inputs from the striatum and the globus pallidus. To address this question we have used two different approaches. First, we have developed a double anterograde labelling technique suitable for both light and electron microscopy and combined this procedure with the retrograde transport of lectin-conjugated horseradish peroxidase in order to retrogradely label the nigrocollicular cells. Second, we have combined the anterograde transport of Phaseolus vulgaris-leucoagglutinin from the globus pallidus and immunocytochemistry for DARPP-32 as a marker for the striatal terminals, with the retrograde transport of lectin-conjugated horseradish peroxidase from the superior colliculus. In the double anterograde labelling experiment, biocytin was injected in the striatum, Phaseolus vulgaris-leucoagglutinin in the globus pallidus and lectin-conjugated horseradish peroxidase in the superior colliculus. Following these injections, rich plexuses of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals were found in the ventral two-thirds of the substantia nigra. The biocytin-positive terminals (striatonigral) were generally small and formed rich plexuses without any apparent neuronal association whereas the Phaseolus vulgaris-leucoagglutinin-labelled terminals (pallidonigral) were much larger and formed baskets around the perikarya of retrogradely and non retrogradely labelled cells in the substantia nigra reticulata. In areas of the substantia nigra reticulata where the fields of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals overlapped, the perikarya and the proximal dendrites of retrogradely and non retrogradely labelled cells were found to be apposed by numerous Phaseolus vulgaris-leucoagglutinin-immunoreactive pallidonigral terminals and a few biocytin-labelled striatonigral terminals. In the sections prepared for electron microscopy, the biocytin was localized using 3,3'-diaminobenzidine tetrahydrochloride whereas Phaseolus vulgaris-leucoagglutinin was localized using benzidine dihydrochloride. It was thus possible to distinguish the biocytin- from the Phaseolus vulgaris-leucoagglutinin-labelled terminals in the electron microscope by the texture of the reaction product associated with them.4+ Examination of 231 biocytin-labelled (striatonigral) terminals and 105 Phaseolus vulgaris-leucoagglutinin-immunoreactive (pallidronigral) terminals revealed that the striatonigral terminals were generally small, contained few mitochondria and formed symmetric synapses predominantly with the distal dendrites (77%) and far less frequently with the perikarya (3%) of substantia nigra reticulata cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differential processing patterns of motor information via striatopallidal and striatonigral projections

The functional loop linking the frontal lobe and the basal ganglia plays an important role in the control of motor behaviors. To delineate the principal features of motor information processing in the cortico-basal ganglia loop, the present study aimed at investigating how corticostriatal inputs from the primary motor cortex (MI) and the supplementary motor area (SMA) are transposed onto the pallidal complex and the substantia nigra. In macaque monkeys, stimulating electrodes were chronically implanted into identified forelimb representations of the MI and SMA. Subsequently, the distribution of neurons exhibiting orthodromic responses was examined in the caudal putamen to demarcate striatal zones receiving inputs separately or confluently from the MI and SMA. Finally, anterograde double labeling was performed by paired injections of tracers into two of three identified zones: the MI-recipient zone, SMA-recipient zone, and the convergent zone. Data have revealed that inputs from the MI-recipient and SMA-recipient striatal zones were substantially segregated in the pallidal complex and that those from the convergent zone were distributed to fill in blanks made by terminal bands derived from the MI and SMA. On the other hand, striatonigral inputs from the SMA-recipient and convergent zones of the putamen largely overlapped, while the input from the MI-recipient zone was minimal. The present results clearly indicate that the mode to process corticostriatal motor information through the striatopallidal and striatonigral projections is target-dependent, such that the parallel versus convergent rules govern the arrangement of striatopallidal or striatonigral inputs, respectively.     

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.     

Substance P: localization within paleostriatal-tegmental pathways in the pigeon

Immunohistochemical techniques were used to determine the distribution of substance P-like immunoreactivity within the paleostriatal complex and within the projection targets of the paleostriatal complex in the pigeon. The density of substance P-like immunoreactivity was found to be much greater in the paleostriatal complex than in immediately overlying portions of the telencephalon (such as the neostriatum and ectostriatum). The small-celled zone of the paleostriatal complex (equivalent to the mammalian caudate-putamen) is characterized by the presence of numerous neurons and fibers that show intense substance P-like immunoreactivity. A higher density of neurons containing substance P-like immunoreactivity was observed within the more medial subdivision of the small-celled zone of the paleostriatal complex (termed the lobus parolfactorius), than in the more lateral subdivision of the small-celled zone of the paleostriatal complex (termed the paleostriatum augmentatum). Many of the substance P-containing fibers within the neuropil of lobus parolfactorius and paleostriatum augmentatum appeared to represent the processes of the substance P-containing neurons of those regions. A dense network of seemingly thick, coarse substance P-containing fibers was observed in the large-celled zone of the avian paleostriatal complex (termed the paleostriatum primitivum). A few medium-sized substance P-containing neurons were evident in the latter area.In addition to fine substance P-containing fibers, numerous thick substance P-immunoreactive fibers were observed in the lobus parolfactorius. The substance P-containing fibers of this region appeared to contribute to a dense substance P-containing fiber plexus in the ventromedial floor of the telencephalon. This region, through which the medial forebrain bundle courses, has been termed the ventral paleostriatum by Kitt &; Brauth.³⁶ The medial forebrain bundle could be traced as a substance P-positive fiber bundle from within the ventral paleostriatum to the midbrain tegmentum. Within the midbrain tegmentum, the fibers of the medial forebrain bundle could be traced into prominent substance P-immunoreactive terminal fields over the cell bodies and neuropil of the catecholaminergic cell groups of the tegmentum, including the ventral tegmental area of Tsai and the nucleus tegmentipedunculopontinus. Within the latter nucleus, substance P-containing fibers and terminals were most densely concentrated within the dorsomedial portion of the nucleus. Kitt &; Brauth³⁶have recently shown by horseradish peroxidase and autoradiographic pathway tracing techniques that the lobus parolfactorius projects to the portions of the ventral tegmental area and nucleus pedunculopontinus that were observed to contain a dense field of substance P-containing fibers and terminals. Unilateral knife cuts of the medial forebrain bundle at rostral diencephalic levels were found to eliminate nearly totally the substance P-immunoreactivity from the neuropil of the ventral tegmental area and nucleus pendunculopontinus on the ipsilateral side of the brain.The present findings argue that, as in mammals, portions of the small-celled zone of the basal ganglia (or paleostriatal complex) in birds may utilize substance P as a neurotransmitter or modulator in their projections upon catecholaminergic cell groups of the midbrain. The present data further suggest that the lobus parolfactorius and paleostriatum augmentatum together in birds are to be considered equivalent to the mammalian caudate-putamen and nucleus accumbens. Previous studies had only emphasized the similarity of paleostriatum augmentatum to the mammalian caudate-putamen.^4,33     

Enkephalin innervation of the paraventricular nucleus of the hypothalamus: distribution of fibers and origins of input

The opioid peptide enkephalin emerges as a major neuromodulator in the regulation and integration of the physiologic response in stressful conditions. The paraventricular nucleus of the hypothalamus is a coordinating center of neuroendocrine and autonomic functions. However, the detailed distribution of the enkephalin fibers and terminals in the paraventricular nucleus and the sources of enkephalinergic innervation are not well defined. In the present study, we used immunocytochemistry for the proenkephalin-derived octapeptide met-arg⁶-gly⁷-leu⁸ enkephalin to determine the distribution of enkephalin-immunoreactive fibers and somata within paraventricular nucleus. Without colchicine pretreatment, enkephalinergic fibers were prominent mainly in the ventromedial part of the parvicellular subdivision of the paraventricular nucleus, appearing in coronal sections as a dense collection of short segments of enkephalin-immunoreactive fibers. In the periventricular portion of the paraventricular nucleus, enkephalin-immunoreactive fibers produced a moderate plexus of short enkephalin-immunoreactive fibers dorsoventrally oriented. With colchicine treatment, a dense cluster of enkephalin-immunoreactive cell bodies was located in the dorsomedial and the dorsal parts of the parvicellular subdivisions. These enkephalin-immunoreactive neurons were small (< 10 μm) to medium sized (10–15 μm), with round and elongated shapes. Retrograde transport of wheat germ-conjugated gold particles. WGA-apoHRP-Au, from the paraventricular nucleus, combined with immunocytochemistry for enkephalin revealed that the major sources of extrahypothalamic enkephalin afferents to the paraventricular nucleus are provided by enkephalin neurons neurons in the lateral reticular nucleus and the paragigantocellularis reticular nucleus of the medulla (20% of retrogradely labeled neurons within this nucleus were double labeled) and in the nucleus solitary tract (10% of retrogradely labeled neurons within thisnucleus were double labeled). Retrogradely labeled enkephalin neurons were also observed in the medial preoptic area, median preoptic nucleus, dorsomedial hypothalamic nucleus, lateral septum and hypothalamic arcuate nucleus. These enkephalinergic pathways from the medulla and the forebrain could represent an anatomical substrate underlying the opioid effects on paraventricular neurons during physiological processes, such as a cardiovascular regulation, feeding or stress responses.